Ocean and water pollution

Water is the planet’s great solvent. It dissolves minerals from rock, carries nutrients to forests and fish, and cleans itself as it moves. For most of history that was enough: people poured waste into rivers and nature diluted it. At today’s scale, with more than eight billion people and industrial farming on every continent, dilution stopped working long ago. What we spill on the land reaches the sea.

How water becomes polluted

Pollution arrives in two ways. Point sources come out of a pipe: a sewage outfall, a factory drain, a mine. They are easy to find and, with permits and treatment, easy to fix. Diffuse sources come from everywhere at once: fertiliser and manure washing off fields, oil and tyre dust washing off roads, pesticides drifting from crops. They are harder, because no single pipe can be closed.

The main pollutants are:

• Nutrients. Nitrogen and phosphorus from fertilisers, manure and sewage. In water they feed algae, which bloom, die and rot, using up the oxygen fish need.
• Pathogens. Bacteria, viruses and parasites from untreated sewage and animal waste. They cause cholera, dysentery, typhoid and diarrhoeal disease.
• Chemicals. Heavy metals such as mercury and lead, industrial solvents, pesticides, pharmaceuticals and the so-called forever chemicals (PFAS), which barely break down at all.
• Sediment and heat. Soil from erosion clouds rivers and smothers reefs; warm water from power stations lowers oxygen further.

Who is affected

Everyone drinks downstream of someone. According to the World Health Organization, at least 1.7 billion people used a drinking-water source contaminated with faeces in 2022, and 2.2 billion still lacked safely managed drinking water. The burden falls hardest on children: unsafe water, sanitation and hygiene remain a leading cause of diarrhoeal deaths among the youngest.

Behind those numbers is sanitation. In 2022, 57 percent of the world’s people used a safely managed toilet. More than 1.5 billion had no basic sanitation at all, and 419 million still defecated in the open, in street gutters, behind bushes or straight into rivers and canals. In 2020, 44 percent of household wastewater was discharged without safe treatment (WHO, 2024). Where there is no sewer, the river becomes one.

Ecosystems pay too. Where nutrient-rich rivers meet the sea, oxygen can fall so low that fish and shellfish suffocate. These dead zones now number in the hundreds; one of the largest forms every summer in the Gulf of Mexico, fed by the Mississippi. Around the world, the open ocean has lost oxygen as well, and low-oxygen coastal sites have multiplied since the middle of the twentieth century (Breitburg et al., 2018).

A dead zone is a crime scene with thousands of suspects and no single weapon.

The rivers that carry the most

A handful of rivers show the whole problem at once: sewage, factory waste and plastic, all in the same water, in cities that grew faster than their pipes, bins and treatment plants. Naming them is not about blame. The people who live beside these rivers are the first to suffer from them, and many of them are working hardest to bring them back.

Sewage and daily life

The Pasig runs through Metro Manila, home to more than 13 million people. Much of the city’s rubbish and sewage reaches it through small creeks and canals lined with homes that have no sewer connection and no regular waste collection. When the monsoon rains arrive, everything on the ground is washed downstream within hours. The same pattern repeats along the Klang in Kuala Lumpur, the Ulhas and Mithi in Mumbai, and hundreds of smaller city rivers in the tropics.

Factories: tanneries and dyes

In Dhaka, the tanneries of Hazaribagh released an estimated 21,600 cubic metres of untreated effluent every day, laden with chromium, sulphur and ammonium, into channels that drain to the Buriganga (Human Rights Watch, 2012). Workers, many of them children, and neighbours bore the health effects first; the leather went to shoes and bags sold around the world.

On Java, the Citarum is a main source of drinking water and irrigation for West Java. A 2025 study reports that the river received about 35.5 tonnes of human waste every day in 2017, and that about 90 percent of the 3,236 textile factories along it lacked adequate wastewater treatment, so dyes and chemicals went straight into the water (Marselina et al., 2025). In 2018 Indonesia launched Citarum Harum, a national programme to restore the basin that brings together national and local government, the armed forces, businesses and communities.

The Ganges is sacred to hundreds of millions of people and supplies water to a large part of India and Bangladesh. Along its course, industries such as tanneries and distilleries add their waste to the sewage of fast-growing towns. India’s Namami Gange programme, started in 2014, is building and monitoring sewage treatment plants along the river and its tributaries (National Mission for Clean Ganga).

Plastic

Plastic is the most visible of these pollutants, and the one we can now estimate river by river. Two major studies used computer models, checked against field measurements, to estimate how much plastic each river carries to the sea:

• Lebreton et al. (2017) estimated 1.15 to 2.41 million tonnes a year from all rivers, with the top 20 rivers carrying two thirds, led by the Yangtze, the Ganges and the Xi.
• Schmidt et al. (2017) went further, suggesting that just 10 rivers carry 88 to 95 percent of the global load. This “ten rivers” claim spread widely, but the authors themselves warned of high uncertainty, and newer work does not support it.
• Meijer et al. (2021) followed waste from where it is dropped to the nearest stream and on to the sea, taking into account rainfall, land use and distance. They found that more than 1,000 rivers carry 80 percent of river plastic to the ocean, 0.8 to 2.7 million tonnes a year in total, and that small rivers running through big cities are among the worst.

The ranking

These are the ten river mouths with the highest estimated plastic emissions in the newer model. The figures are model midpoints for conditions around 2015, rounded to the nearest hundred tonnes.

These tables describe the past. Both models use data for around 2015, before many recent clean-up programmes took effect, and neither has been rerun for today’s rivers. The figures for the Yangtze, the Xi and the Huangpu, for example, describe China’s rivers ten years ago, when its national clean-up had only just begun, and the Pasig figure predates Manila’s newest programme. What happened next, river by river, is told in rivers that came back around the world below.

Rank	River	Country	Estimated plastic to the sea (tonnes a year)	Source
1	Pasig	Philippines	62,600	Meijer et al. 2021
2	Tullahan	Philippines	13,500	Meijer et al. 2021
3	Ulhas	India	13,400	Meijer et al. 2021
4	Klang	Malaysia	12,800	Meijer et al. 2021
5	Meycauayan	Philippines	12,400	Meijer et al. 2021
6	Pampanga	Philippines	9,300	Meijer et al. 2021
7	Libmanan	Philippines	7,100	Meijer et al. 2021
8	Ganges	India and Bangladesh	6,200	Meijer et al. 2021
9	Rio Grande de Mindanao	Philippines	5,300	Meijer et al. 2021
10	Agno	Philippines	4,600	Meijer et al. 2021

The older model ranks large river basins instead, with a range for each:

Rank	River	Country	Midpoint (tonnes a year)	Range	Source
1	Yangtze	China	333,000	310,000 to 480,000	Lebreton et al. 2017
2	Ganges	India and Bangladesh	115,000	105,000 to 172,000	Lebreton et al. 2017
3	Xi	China	73,900	64,600 to 114,000	Lebreton et al. 2017
4	Huangpu	China	40,800	33,500 to 67,300	Lebreton et al. 2017
5	Cross	Nigeria and Cameroon	40,300	33,800 to 65,000	Lebreton et al. 2017
6	Brantas	Indonesia	38,900	32,300 to 63,700	Lebreton et al. 2017
7	Amazon	Brazil, Peru, Colombia and Ecuador	38,900	32,200 to 63,800	Lebreton et al. 2017
8	Pasig	Philippines	38,800	32,100 to 63,700	Lebreton et al. 2017
9	Irrawaddy	Myanmar	35,300	29,700 to 56,900	Lebreton et al. 2017
10	Solo	Indonesia	32,500	26,500 to 54,100	Lebreton et al. 2017

How sure are these numbers? Not very, and it is important to say so. Both are models: nobody has weighed the plastic leaving a thousand river mouths. Meijer’s own global total spans a factor of more than three, and the authors describe their model as accurate to within about a factor of ten when compared with field measurements; the Pasig sits on the edge of that band. The two models also disagree about specific rivers. The Ganges drops from 115,000 tonnes a year in the older model to about 6,200 at its main mouth in the newer one, because the newer model gives plastic dropped far inland a much smaller chance of reaching the sea: much of it is caught on riverbanks, behind dams and in sediment along the way. Other rivers often named in public debate, such as the Chao Phraya in Bangkok, the Kelani in Colombo and the Mithi in Mumbai, also appear among the 50 largest emitters in the newer model’s published list. What the two studies agree on is the pattern: most river plastic comes from places where waste is not collected, where people live close to rivers, and where heavy rain washes the land.

Rivers that came back around the world

The rivers in the tables above are not a lost cause. Rivers that were written off have been brought back on four continents, in rich countries and in poorer ones, under very different governments. None of them was cleaned by one invention or one law. Each case below answers the same four questions: what went wrong, what was done, what was measured, and what is not solved yet. They are listed roughly in the order in which their main clean-up began.

The Thames, London

What went wrong. London’s sewers and treatment works could not keep up with the city’s growth. By the 1950s so little oxygen was left in parts of the tidal Thames that in 1957 they were declared biologically dead. The Victorian sewers also carry rainwater, and when it rains hard they still overflow into the river.

What was done. A clean-up of the river’s sewage works began in 1960 (BBC, 2001). In 2014 Thames Water finished upgrading five treatment works, at Beckton, Crossness, Riverside, Long Reach and Mogden. In 2016 the 7 km Lee Tunnel began capturing more than 5 million tonnes of sewage a year that used to spill from the largest overflow. The 25 km Thames Tideway Tunnel, a £4.6 billion project paid for through Thames Water customers’ bills, now links to it, so that the system can store 1.6 million cubic metres of storm sewage; it has been fully connected and working since February 2025, and is expected to cut spills into the tidal river from more than fifty in a typical year to about five (Thames Water; Tideway).

What was measured. The first salmon returned in 1974, and by 2001 the river supported 115 species of fish (BBC, 2001). The Zoological Society of London’s 2026 health check found dissolved oxygen rising over the long term from 2007 to 2024 and phosphorus falling since the 1990s; seahorses, eels, seals and even small sharks now live in the estuary (ZSL, 2026).

Not solved yet. The same health check found nitrate still rising from treated sewage, and a slight fall in fish species since the early 1990s that needs more research. Upstream of the tunnel, Thames Water’s overflows and treatment works spilled sewage for 298,081 hours in 2024, up from 196,414 in 2023, according to an analysis of the company’s monitoring data (The Guardian, 2025). Across England, spills fell by 35 percent in 2025, which the Environment Agency says was largely due to a dry year (Environment Agency, 2026).

The Cuyahoga, Cleveland, and the US Clean Water Act

What went wrong. On 22 June 1969 a spark from a passing train set fire to an oil slick on the Cuyahoga. It was not the first time: the local sewer district counts 13 fires on the river before 1969 (NEORSD). In the 1970s more than 9 billion gallons of combined sewage and rainwater a year overflowed from the area’s sewers into the river and Lake Erie (NEORSD).

What was done. Cleveland’s voters had already approved a 100 million dollar bond to clean up the city’s waterways, and the mayor took reporters to the river and testified to Congress (NPR, 2019). In 1972 Congress passed the Clean Water Act, which made it unlawful to discharge pollution from a pipe into US waters without a permit and paid for new sewage treatment plants (US EPA). In 1987 the river was named a Great Lakes Area of Concern with nine official problems to fix. Since 2011 the sewer district’s Project Clean Lake, a 3 billion dollar, 25-year programme agreed with regulators, has been building tunnels and storage to cut overflows from about 4.5 billion gallons a year to 494 million by 2036 (NEORSD).

What was measured. Overflows had already halved by 2000. By December 2025, 76 of Project Clean Lake’s 78 projects were finished or under way, removing 2 billion gallons of overflow a year. Fish came back: more than 60 species were found in the river by 2014 (NEORSD). The EPA has removed five of the nine official problems: poor appearance (2017), limits on eating fish (2019), algae (2021), fish tumours (2023) and beach closings (2024) (US EPA).

Not solved yet. Four problems remain: fish and wildlife populations, life on the river bed, dredging of the navigation channel and loss of fish habitat. Behind the Gorge Dam, built in 1911, about 865,000 cubic yards of contaminated sediment are being cleaned up from 2025 before the dam can be removed (US EPA).

The Yarra, Melbourne

What went wrong. Before Melbourne’s sewage was piped to a treatment farm at Werribee from 1897, the Yarra was described as one of the world’s dirtiest rivers (Melbourne Water). As the city grew, farms, streets and stormwater drains kept adding pollution.

What was done. Sewerage came first, and the river has improved greatly since the 1970s and 1980s (same source). In 2017 Victoria passed the Yarra River Protection (Wilip-gin Birrarung murron) Act, a law that treats the river as one living and integrated natural entity, and set up the Birrarung Council to advise on it (Victorian legislation).

What was measured. The upper Yarra supplies about 70 percent of Melbourne’s drinking water (Melbourne Water). Since December 2013 the state environment agency has tested bacteria at four popular spots and publishes swimming forecasts for them (EPA Victoria).

Not solved yet. Water quality still gets worse downstream, because of farming, urban development and stormwater (Melbourne Water). Two of the forecast sites, Kew and Launching Place, are always forecast as poor for swimming (EPA Victoria).

Minamata Bay, Japan

What went wrong. For years a chemical factory run by the Chisso company released methylmercury, a by-product of making acetaldehyde, into Minamata Bay. Fish and shellfish absorbed it, and so did the people and animals who ate them. The poisoning was officially identified as a disease in 1956. The factory stopped the process in May 1968, and the government confirmed the cause that September (Ministry of the Environment of Japan).

What was done. In 1974 nets were stretched across the bay to keep contaminated fish from leaving it. From 1977 to 1990, about 1.5 million cubic metres of sediment containing more than 25 parts per million of mercury were dredged and sealed into 58 hectares of reclaimed land. The work cost about 48 billion yen, of which Chisso paid about 30 billion and the national and prefectural governments about 9 billion each (same source).

What was measured. Mercury levels in seven species of fish stayed below the provisional limits for three years in a row, and in 1997 the governor declared the bay safe and the nets were taken away (same source).

Not solved yet. The bay recovered within decades; the people have not. By December 2024, 3,000 people had been officially certified with Minamata disease, including those of a second outbreak in Niigata, and 304 of them were still alive (National Institute for Minamata Disease). About 11,000 more people qualified for relief under a political settlement reached in 1995, more than 48,000 applied under a relief law passed in 2009 (Ministry of the Environment of Japan), and courts are still deciding claims: in 2023 an Osaka court recognised all 128 plaintiffs in one case, while in 2024 a Kumamoto court rejected 144 because the time limit had passed (Asahi Shimbun, 2024).

The Singapore River

What went wrong. By the 1970s the Singapore River and the Kallang Basin were full of rubbish, sewage and abandoned boats. Waste from pig and duck farms, backyard trades, street hawkers and homes without sewers flowed straight into the water.

What was done. On 27 February 1977 Prime Minister Lee Kuan Yew set a target of ten years to clean the river. Across the river’s catchment and the neighbouring Kallang Basin, thousands of squatter families were resettled, and 610 pig farms, about 500 duck farms, more than 2,800 backyard trades and about 5,000 street hawkers were moved. The 800 cargo lighters that crowded the river were moved to Pasir Panjang by 1983. The National Library Board puts the cost at about 300 million Singapore dollars, not counting resettlement compensation (National Library Board).

What was measured. By the time the campaign ended in 1987, fish and prawns were breeding in the river again (National Library Board). The Marina Barrage, finished in 2008, turned the river mouth into a freshwater reservoir in 2010, with a catchment of 10,000 hectares (PUB).

Not solved yet. We could not find a published long-term record of the river’s own water quality. A 2015 study notes that the new reservoir, a former estuary, still suffers from high salinity (Galelli et al., 2015).

The Mersey, North West England

What went wrong. Two centuries of industry and the sewage of millions of people made the Mersey one of the most polluted rivers in Europe, and in 1985 it was called the most polluted estuary in the United Kingdom (Mersey Basin Campaign). In the 1970s, long stretches of the upper estuary had no oxygen at all in summer, at every state of the tide (Jones, 2006).

What was done. The Mersey Basin Campaign ran for 25 years, from 1985 to 2010, bringing together government, the water company, industry and community groups (Mersey Basin Campaign). New and upgraded treatment works and industrial discharge controls followed: by 2006 more than £1 billion had been spent (Jones, 2006).

What was measured. The daily load of organic pollution (BOD) entering the estuary fell from more than 300 tonnes in 1972 to just over 50 tonnes in 2000 (Jones, 2000). The lowest oxygen recorded in the upper estuary rose to 48 percent of saturation in 2001, 58 percent in 2002 and 65 percent in 2003. In November 2001 salmon were caught in the river for the first time in about half a century, and 26 were trapped at Woolston Weir in the autumn of 2002 (Jones, 2006).

Not solved yet. In summer, oxygen in the stretch of the Manchester Ship Canal that salmon must pass was still very poor, around 20 percent, which blocks fish on their way upstream (same source). Researchers studying the estuary’s recovery also point to continuing concern about old pollutants passing up the food chain (Hawkins et al., 2020).

Boston Harbor

What went wrong. Until the 1990s, Boston’s sewage reached its harbour with only basic treatment, and sewage sludge was dumped into it every day. In 1987, 84 combined sewer overflows still released untreated sewage and rainwater into the harbour and its rivers (MWRA).

What was done. In 1985 a federal court ordered the region’s new water authority to build proper sewage treatment. Sludge dumping into the harbour stopped in 1991, a new treatment plant on Deer Island opened in stages from 1995, and in 2000 a 9.5-mile tunnel moved the treated outflow far out into the deep water of Massachusetts Bay (MWRA). The Boston Harbor Project cost about 3.8 billion dollars (MWRA). A separate plan of about 906 million dollars closed 34 of the 84 overflows and is designed to cut the volume spilled in a typical year by 88 percent (MWRA).

What was measured. The water authority monitors more than 70 points in the harbour and its rivers and publishes the data, and the state tests the beaches every summer (MWRA). The Charles River’s grade has risen from D to B or better since 2004 (MWRA), and in 2025 every metropolitan beach from Nahant to Nantasket scored above 80 percent for safe swimming, a first (Save the Harbor/Save the Bay, 2025).

Not solved yet. In a typical year the Charles River meets the bacteria standard for swimming only 48 percent of the time, and some overflows still miss their targets (MWRA, 2023). A draft updated overflow plan is open for public comment until 30 October 2026 (City of Somerville).

The Rhine

What went wrong. For decades the Rhine carried the waste of one of the world’s most industrial regions. On 1 November 1986 a fire at a Sandoz warehouse near Basel washed up to 30 tonnes of pesticides into the river and killed fish along hundreds of kilometres.

What was done. The countries along the river answered with the Rhine Action Programme in 1987: halve the discharges of 40 dangerous chemicals within ten years, and make the river clean enough for salmon to return (International Commission for the Protection of the Rhine). Treatment plants were built and upgraded, and fish passes were opened around the big dams, at Iffezheim in 2000 and Gambsheim in 2006 (ICPR).

What was measured. Heavy metals in the river fell significantly between 1987 and 2000 (ICPR). The nitrogen the Rhine carries to the sea fell from more than 443,000 tonnes in 1985 to about 272,000 tonnes in 2016 (ICPR). Salmon began swimming up from the North Sea into the River Sieg in 1990 and have bred there naturally since 1994; by around 2000, 63 fish species were back, and fish from the Rhine, apart from eel, were safe to eat again (ICPR, Salmon 2020). The commission now lists 71 species, with every fish known from the river’s past back except the European sturgeon (ICPR).

Not solved yet. The salmon are still few: the fish pass at Koblenz counted 11 returning adults in 2025 (ICPR counts). About two thirds of the nitrogen now comes from farming and other diffuse sources, heavy metals from diffuse sources are still too high, and treatment plants do not remove most traces of medicines and other micropollutants; the countries aim to cut these by at least 30 percent by 2040 (ICPR).

The Danube and the Black Sea

What went wrong. Fertiliser, manure and sewage from one of Europe’s largest river basins poured nutrients into the north-western Black Sea. From the early 1970s, water near the sea bed ran out of oxygen every year, and in 1983 the low-oxygen area covered about 20,000 square kilometres (Capet et al., 2013).

What was done. In 1994 the countries of the basin signed the Danube River Protection Convention in Sofia, and since 1998 they have worked together through the International Commission for the Protection of the Danube River, with shared monitoring and a basin plan (ICPDR).

What was measured. The commission reports that nitrogen emissions in the basin fell by about 30 percent and phosphorus by about 50 percent over roughly 15 years (ICPDR). The Black Sea’s low-oxygen zone shrank, although a detailed study found the recovery in the late 1990s was smaller than first thought, and came mainly in the 2000s (Capet et al., 2013).

Not solved yet. In the basin’s 2021 plan, only 24 percent of river length had good ecological status and 36 percent good chemical status, 624 barriers still blocked fish migration, the European sturgeon was extinct in the basin, and nutrient loads were still above those of the 1960s (ICPDR, 2021).

The Pasig, Manila

What went wrong. The Pasig carries the waste of a metropolitan area of more than 13 million people, and was declared biologically dead in the 1990s (GMA News, 2018). It tops the newer model’s list of rivers carrying plastic to the sea, although its authors note that the model overestimates the Pasig compared with measurements made in 2019 (Meijer et al., 2021).

What was done. From 1999 to 2019 the Pasig River Rehabilitation Commission cleared the banks and creeks. By 2018, when it won the first Asia RiverPrize, 18,719 families living on the riverbanks had been resettled and 17 of the river’s 47 tributaries had been developed, starting with a pilot at Estero de Paco in 2010 (GMA News). The commission was abolished in 2019 (Philstar, 2019). Since January 2024 a new programme, Pasig Bigyang Buhay Muli, has been building a riverside esplanade, whose fourth phase opened in October 2025 (ABS-CBN, 2025).

What was measured. The commission’s own report shows that organic pollution (BOD) in the river averaged 30.79 milligrams per litre from 2009 to 2014, against a standard of 7, and rose from 23.09 in 2012 to 39.03 in 2014; oxygen averaged only 2.85 milligrams per litre (PRRC, 2014). A 2018 state audit found that 96 percent of the funds for clearing waterways had been used, with between 1 and 28 percent of the planned work done (Rappler, 2018).

Not solved yet. Most. We could not find official water-quality measurements from after 2014, so we cannot say whether the river is recovering today. The creeks show that it can be done street by street; the whole river has not yet followed.

Cheonggyecheon, Seoul

What went wrong. The stream in the centre of Seoul had been covered with concrete and an elevated motorway.

What was done. Between 2003 and 2005 the city tore down the motorway and opened up 5.8 kilometres of stream, at a total cost of about 380 million US dollars (Landscape Architecture Foundation, 2011).

What was measured. Between 2003 and 2008 the number of fish species rose from 4 to 25, birds from 6 to 36, insects from 15 to 192 and plants from 62 to 308. The air along the stream is 3.3 to 5.9 °C cooler than on a parallel road (Landscape Architecture Foundation), and in 2025 surveyors recorded 33 species of fish, the most since the restoration (The Korea Herald, 2025).

Not solved yet. The stream is largely artificial: more than 48,000 tonnes of water a day are pumped into it, mostly treated water from the Han River plus groundwater, and its upkeep costs about 2.9 billion won a year (The Guardian, 2025). In 2011, coliform bacteria in the stream measured many times the standard for swimming (The Korea Herald, 2011).

The Ganga, India

What went wrong. The Ganga is sacred to hundreds of millions of people and supplies water to a large part of India and Bangladesh. Along its course, industries such as tanneries and distilleries add their waste to the sewage of fast-growing towns.

What was done. India’s Namami Gange programme, started in 2014, is building and monitoring sewage treatment plants along the river and its tributaries (National Mission for Clean Ganga). Its budget was 20,000 crore rupees to March 2021 and 22,500 crore rupees for a second phase to 2026. By March 2026, 21,340 crore rupees had been spent and 355 of 524 approved projects completed (Press Information Bureau, 2026), and by March 2025 treatment plants able to handle 3,446 million litres of sewage a day had been built or rehabilitated (Press Information Bureau, 2025).

What was measured. Faecal bacteria have fallen at the monitored sites the government reports: the median count at Assi Ghat in Varanasi fell from 2,500 per 100 millilitres in 2014 to 790 in 2025, and at Gandhi Ghat in Patna from 5,400 to 2,200, against a bathing limit of 2,500 (Press Information Bureau, 2026).

Not solved yet. In 2025 the bathing standard for faecal bacteria was met only in certain stretches of Uttar Pradesh, Bihar and West Bengal, and organic pollution was too high from Farrukhabad to Kanpur and from Mirzapur to Ghazipur (same source). During the Maha Kumbh festival in 2025, the first report of the Central Pollution Control Board found the water at monitored sites unfit for bathing on several occasions; a revised report later gave a median within the limit (The Hindu, 2025).

China’s rivers and the Yangtze

What went wrong. In 2015 only 64.5 percent of China’s national monitoring points on rivers and lakes had water of Grade I to III, the grades that can be treated for drinking, and 8.8 percent were worse than Grade V, fit for almost nothing (Ministry of Environmental Protection, 2016). In March 2013 more than 16,000 dead pigs had been pulled from the Huangpu and its tributaries upstream of Shanghai, a source of the city’s tap water, after farms upstream dumped the carcasses in the river (The Guardian, 2013).

What was done. In April 2015 the State Council issued an Action Plan for Water Pollution Prevention and Control, known as the “Water Ten”, with targets for 2020: more than 70 percent of water in the seven main river basins at Grade III or better, polluting small factories closed, livestock farms moved away from sensitive water and about 95 percent of city sewage treated (State Council, 2015). From 2016 every river and lake was given a “river chief”, a named official responsible for its water and assessed on the results (General Office of the CPC Central Committee and State Council, 2016; Water Pollution Prevention and Control Law, Article 5). By 2018, 97.8 percent of larger industrial parks had central wastewater treatment with online monitoring, and by 2019 cities had cleaned up 2,513 of the 2,899 “black and smelly” urban water bodies they had identified (Ministry of Ecology and Environment, 2018 and 2019 bulletins). A Yangtze River Protection Law, in force since March 2021, bans new chemical plants within one kilometre of the river and its tributaries (Yangtze River Protection Law), and commercial fishing in the Yangtze has been banned for ten years from 2021, with support for the fishers who stopped (Xinhua, 2026).

What was measured. By 2025, 91.4 percent of national monitoring points were at Grade I to III and 0.6 percent were worse than Grade V; in the Yangtze basin, 98.9 percent of 1,016 points were at Grade I to III (Ministry of Ecology and Environment, 2026). The number of Yangtze finless porpoises rose from about 1,249 in the 2022 survey to 1,426, and 351 fish species were recorded in the basin in 2021 to 2025, 43 more than before the fishing ban (Xinhua, 2026).

Not solved yet. In 2025, 28.4 percent of major lakes and reservoirs were still over-fertilised, and the largest algal bloom on Taihu covered a fifth of the lake; phosphorus remains the main pollutant in the Yangtze main stream (Ministry of Ecology and Environment, 2026). The water grades do not measure plastic: a phased ban on some single-use plastics began in 2020 (NDRC and Ministry of Ecology and Environment, 2020), but we could not find a new measured estimate of the plastic the Yangtze carries to the sea. The monitoring network also grew from 967 points in 2015 to 3,641 from 2021, so early and late figures are not strictly comparable.

The Seine, Paris

What went wrong. Swimming in the Seine was banned in 1923. Paris’s old sewers carry both sewage and rainwater, and on rainy days they overflow into the river; many homes upstream were also wrongly connected to rainwater drains. By the 1970s only about three species of fish were found in the river around Paris (France 3 / AFP, 2025).

What was done. Since 2015 a bathing plan has invested more than 1.4 billion euros in storage basins, sewer repairs, treatment plants and the correction of about 23,000 faulty household connections; one storage basin at Austerlitz alone holds 50,000 cubic metres and has worked since May 2024 (City of Paris). The Olympic triathlon and marathon swimming were held in the river in 2024, though rain forced delays (France 24, 2024).

What was measured. On 5 July 2025 three public bathing sites opened, at Bras Marie, Grenelle and Bercy (France 24, 2025). In 2026 they welcomed about 120,000 bathers, 20 percent more than in 2025 (City of Paris, 2026). Between 35 and 40 fish species now live in the Seine around Paris, according to the region’s sanitation authority, including the bullhead, which has returned (France 3 / AFP).

Not solved yet. Rain still makes the old sewers overflow, so the sites open only when the current, the water quality and the weather allow, and the 2026 season ended early because of the weather (City of Paris). Invasive gobies are now among the most common fish caught (France 3 / AFP).

What the recoveries have in common

Read side by side, the stories rhyme. Often a shock made people care: a burning river, a poisoned bay, a chemical fire, a river full of dead pigs. Then came rules with deadlines, named people responsible, money for pipes and treatment plants, and monitoring that anyone can check. None of it was quick. The Thames took more than half a century, the Mersey campaign ran for 25 years, the Rhine is still waiting for its salmon to be many, and people poisoned at Minamata are still asking to be recognised.

Not every programme has worked yet, and the measurements say so as plainly as they record success. But wherever sewage was collected and treated, and factories had to clean what they released, the river answered. Communities along the Pasig, the Citarum and the Ganga are showing it again today, one creek and one neighbourhood at a time.

Why it happens here, and why it is not a local problem

The Meijer study compares two rivers. The Ciliwung, which flows through Jakarta, drains 591 square kilometres, less than half a percent of the Rhine basin in Western Europe, and its basin produces less plastic waste. Yet the Ciliwung was measured sending about 300 tonnes of plastic a year to the sea, and the Rhine about 3 tonnes. The difference is geography and infrastructure: in the Ciliwung basin, the average piece of waste is produced about 1 kilometre from a river and 29 kilometres from the ocean, and tropical rain flushes it through. Nothing about the people is different. Their cities grew faster than their waste systems.

The causes are shared, too:

• Fast urbanisation. Cities in South and Southeast Asia, Africa and Latin America have added hundreds of millions of people in a few decades, often in informal settlements on riverbanks and flood plains, where there are no bins, no collection and no sewers.
• Missing waste services. Collecting and treating waste costs money that cities with low tax revenue struggle to find, and the people who collect it, often informal waste pickers, are rarely paid for the plastic that has no resale value.
• Products designed elsewhere. Single-serving sachets, multi-layer wrappers and cheap packaging are designed and sold by companies whose headquarters are often far away, into places that have no way to recycle them.
• Global trade in waste. For decades, wealthier countries shipped plastic waste abroad for “recycling”. China took in about 45 percent of the world’s traded plastic waste from 1992 until it banned most imports in 2018; high-income countries exported about 70 percent of their plastic waste in 2016 to lower-income countries in East Asia and the Pacific, and about 111 million tonnes will need a new destination by 2030 (Brooks et al., 2018). Some of that waste ends up in the same rivers.

One planet, one ocean

Rivers do not stop at borders, and neither does the sea. A bottle that leaves Manila Bay can ride currents across the Pacific; microplastics have been found from Arctic ice to the deepest trenches. Every coastline receives what other coastlines release, and every country buys and sells the goods whose packaging ends up in the water. There is only one ocean, and we all share it, so there is no such thing as someone else’s river.

A river in Manila is a river of the Pacific. What we do to it, we do to the ocean every one of us depends on.

Europe is not plastic-free

It is tempting to see river pollution as a problem of faraway places. It is not. Europe’s rivers carry less plastic because of decades of investment in collection, landfills and treatment, but plastic still persists in its rivers and seas, and some of the waste it exported came back to the ocean elsewhere.

• The Mediterranean is a plastic trap. It holds about 1 percent of the world’s sea water but about 7 percent of its microplastics, and more than 200 million visitors each year push marine litter up by about 40 percent in summer (WWF, 2018). Floating plastic was found at every site sampled across the basin, at densities comparable to the ocean’s great garbage patches, adding up to an estimated 1,000 to 3,000 tonnes afloat (Cózar et al., 2015).
• Greece and its islands. A survey of 80 Greek beaches found that plastic made up 43 to 51 percent of the litter, and the most common items were cigarette butts, bottle caps, straws, bottles, food wrappers and bags; Greece recycles only about a fifth of the plastic it uses (WWF, 2018). On four beaches of Corfu, an average of about 142 new items per 100 metres washed up every 15 days, mostly carried in by the sea (Prevenios et al., 2018). On Mediterranean islands, litter arriving on beaches rises up to 4.7 times in the tourist season (Grelaud and Ziveri, 2020).

• In the water and in the fish. In the Thermaic Gulf off Thessaloniki, researchers counted about 750,000 microplastic particles per square kilometre of sea surface and found microplastics in all seven fish species they tested (Kermenidou et al., 2023). Plastic bottles pulled from the floor of the Aegean and Ionian seas stayed almost unchanged for about 15 years before they began to break down (Ioakeimidis et al., 2016).
• The great rivers of Europe. The Rhine carried on average about 890,000 microplastic particles per square kilometre of surface, with a peak of 3.9 million near the Rhine-Ruhr cities (Mani et al., 2015). In the Austrian Danube, drifting plastic outnumbered drifting fish larvae, and the river was estimated to carry about 4.2 tonnes of plastic a day towards the Black Sea (Lechner et al., 2014).

The European Union now bans several single-use plastic items and requires producers to pay for cleaning up others under its Single-Use Plastics Directive. These are good steps. But every beach clean on a Greek island shows that plastic, once made, lasts longer than any policy.

What actually works

The good news is that water pollution is one of the problems humanity has already solved, in places, many times over, as the rivers above show. The tools are known:

1. Treat the sewage. Collecting and treating wastewater is the single most effective public-health measure in history. Where treatment plants are built and maintained, waterborne disease collapses.

2. Feed crops, not rivers. Precision fertiliser use, cover crops, and buffer strips of trees and grass along riverbanks can cut nutrient runoff dramatically, and save farmers money on fertiliser.

3. Permit, monitor, publish. Industrial discharges fall when permits set limits, monitoring is continuous and results are public. Transparency works because nobody wants to be the name on the map.
4. Restore wetlands. Wetlands are the planet’s water filters, trapping sediment and removing nitrogen for free.
5. Price pollution. Charging for discharges, and paying farmers for clean-water practices, turns clean water into something the market rewards.
6. Collect every bin, and pay the collectors. Most river plastic starts as waste nobody collected. Regular collection in informal settlements, and fair pay for the waste pickers who already recover much of what is recycled, stop plastic before it reaches the water.
7. Catch it before the sea. Barriers, nets and trash traps on small urban rivers and canals can intercept floating waste close to where it enters. They treat the symptom, not the cause, but on the small city rivers that dominate the ranking they can make a real difference while collection improves.

8. Make the makers responsible. When producers pay for the collection of the packaging they sell, and deposit-return schemes pay people to bring it back, packaging gets designed for reuse and recycling instead of for the river.
9. Clean industry, shared plants. Clusters of tanneries and dye works can share one well-run effluent treatment plant, and buyers of leather and textiles can require clean water as a condition of every order.

Projects you can support

Governments did the heavy lifting in the stories above, but they are not alone. Non-profit organisations catch rubbish in rivers before it reaches the sea, test the water where officials do not, take polluters to court and turn millions of volunteers into data. These are some of the most established ones, each with published results. Please look at what they do, and if you can, give to them directly through their own websites.

• The Ocean Cleanup (Netherlands). A non-profit foundation that builds machines to remove plastic. In rivers, its solar-powered Interceptors, floating barriers and small conveyor barges catch rubbish in some of the most polluting rivers and gullies, from Kingston in Jamaica to the Motagua in Guatemala, Los Angeles and Bangkok, and its “30 Cities” programme aims at 30 of the most polluting coastal cities. At sea, System 03, a floating barrier that funnels plastic into a retention zone that is emptied onto a ship about every four days, has worked in the Great Pacific Garbage Patch since 2023 and caught almost 500,000 kg there. Its public dashboard counts about 65 million kg removed from rivers and oceans in total; the organisation says these automatic counts are checked by the independent firm DNV only from time to time (rivers, oceans, dashboard). Its scientists also produced the river ranking used on this page. Donations go to Stichting The Ocean Cleanup, a registered public-benefit foundation in the Netherlands, or in the US to American Friends of The Ocean Cleanup, a 501(c)(3) charity (FAQ).
• Mr. Trash Wheel (Baltimore, United States). Four googly-eyed trash wheels, launched between 2014 and 2021, sit at the mouths of streams flowing into Baltimore’s harbour. A boom funnels floating litter to each wheel, and a water wheel turned by the current, helped by solar-powered pumps, drives a rake and conveyor into a dumpster. Together they collect about 500 US tons (about 450 tonnes) of rubbish a year, about 90 percent of it washed in by rain storms, and volunteers hand-count the contents of a dumpster each year to help inform anti-litter laws. They are run by the Waterfront Partnership of Baltimore, a 501(c)(3) non-profit; the machines are built and maintained by Clearwater Mills, a Maryland company (trash interception, how it works).

• Waterkeeper Alliance (New York, working worldwide). Born from a group of Hudson River fishermen who fought industrial polluters from 1966, the alliance was founded in 1999 and now links 296 local Waterkeeper groups in more than 40 countries and territories. They patrol their rivers, lakes and coasts and use citizen science, lawsuits and policy work to hold polluters to account (about).
• Ocean Conservancy (Washington, D.C.). Its International Coastal Cleanup has brought more than 19 million volunteers to beaches and waterways, who have picked up more than 400 million pounds of rubbish, and it records every item through the Clean Swell app, so the clean-ups also tell us which products end up in the water.
• Surfrider Foundation (California, with chapters across the United States). Its Blue Water Task Force runs more than 60 volunteer laboratories that test bacteria at more than 600 beaches, bays and creeks, often where official testing stops out of season, and uses the results to push for fixes (Blue Water Task Force).
• Thames21 (London). A registered charity (number 1103997) that brings thousands of volunteers each year to clean and restore London’s 400 miles of rivers and streams, the everyday work behind the Thames recovery described above.

What you can do, and how to take part

Clean rivers are built by governments, water companies and farms, but also by millions of small habits and a few hours of volunteering. Here is what helps, from the kitchen sink to the town hall. When you are ready to do more, the Local Solar System Foundation’s Get Involved page lists local tasks you can take on where you live, and a way to find or start a local chapter. The projects above welcome volunteers as well as donations. Whatever you do, tell us about it through the contribution board, where the Foundation’s Council reviews every contribution.

At home

• Bin the fat. Let cooking fat, oil and grease cool, then scrape it into the bin. They cause more than 20,000 sewer blockages a year on Thames Water’s network alone, 28 percent of all its blockages (Thames Water, 2025). In 2017 a single “fatberg” of fat and wipes under Whitechapel in London grew to 250 metres long and 130 tonnes (BBC, 2017).
• Flush only pee, poo and paper. Wet wipes cause 94 percent of sewer blockages in the United Kingdom, and blocked sewers mean that storm overflows into rivers are used more often (Water UK; Bin the Wipe). Wipes, cotton buds and sanitary products go in the bin.

• Take unwanted medicines back. Do not flush them or throw them away: take them to a pharmacy or a take-back scheme (NHS; US EPA). A study of 258 rivers in 104 countries found at least one medicine at a level considered unsafe for wildlife, or of concern for antibiotic resistance, at more than a quarter of the places sampled (Wilkinson et al., 2022).
• Keep street drains for rain. In many towns, the drains in the street run straight to the nearest river without any treatment (UK government). Never pour paint, motor oil or soapy water from washing the car into one; take paint and oil to a recycling centre.
• Feed the garden, not the river. Use less fertiliser and pesticide, only the recommended amount, keep it away from ponds and streams, and never spread it before rain (US EPA). If you own land beside water, a strip of native plants along the bank filters runoff before it arrives.

Where you live

• Join a clean-up, or organise one. World Cleanup Day falls on 20 September every year, and its organisers say people in 212 countries and territories have taken part (United Nations; World Cleanup Day). Ocean Conservancy’s International Coastal Cleanup and the Marine Conservation Society’s Great British Beach Clean take place every September, and river groups such as Thames21 hold events all year. Record what you pick up, for example in the free Clean Swell app, so that the clean-up also becomes data (Ocean Conservancy).

• Stay safe while you do it. Wear gloves or use a litter picker, start at low tide or a couple of hours after high tide, and never touch syringes, drums or anything that looks dangerous: leave it where it is and report it. As the Marine Conservation Society puts it, if in doubt, don’t lift (MCS organiser guide, 2026).

• Test your river. Citizen-science programmes give you a simple kit, training and a place to share results. FreshWater Watch, run by Earthwatch, has collected more than 70,000 sets of measurements from over 22,000 volunteers around the world. The Rivers Trust’s Big River Watch asks people in the UK and Ireland to watch a river for 15 minutes, twice a year, with a free app. The Riverfly Partnership trains volunteers to monitor small river creatures that are sensitive to pollution. The EarthEcho Water Challenge helps young people test their local water, Water Rangers offers test kits and an open data platform in Canada, Waterwatch supports groups in Australia, and Surfrider’s Blue Water Task Force tests beaches in the United States.

• Report pollution when you see it. Dead fish, sewage, an oily sheen, foam or strange colours: note the place and time, take a photo if it is safe, and call the authority at once. In England, the Environment Agency’s incident line is 0800 80 70 60, day and night (UK government); in Scotland, SEPA takes reports online or on 0800 807060 (SEPA); in Ireland, the national complaints line is 1800 365 123 and most councils accept reports through the See it? Say it! app (EPA Ireland); in the United States, the EPA has an online tip form, and emergencies go to the National Response Center on 1-800-424-8802 (US EPA); in Victoria, Australia, EPA Victoria answers on 1300 372 842 (EPA Victoria). Anywhere else, your local council or national environment agency is the place to start.
• Adopt a stream. Some places run schemes in which a school, a club or a group of neighbours looks after one stretch of river or beach, and checks it regularly; Georgia Adopt-A-Stream in the United States is one long-running example. If there is none near you, propose one as a local task.

With your voice

• Ask for the data. Much of it is already public. In England and Scotland, The Rivers Trust’s sewage map shows every storm overflow and how often it spilled (The Rivers Trust); in Europe, the European Environment Agency publishes results for more than 22,000 bathing sites, 85 percent of them rated excellent in 2025 (EEA); in the United States, the EPA’s How’s My Waterway shows the condition of local rivers and lakes. Where there is no data, ask your council or water utility why not, and what the plan is.
• Support deposit return and producer responsibility. Deposits bring bottles and cans back before they reach a river, and producer schemes make the makers of packaging pay for its collection. Our plastic pollution explainer shows how well they work.

• Back investment in sewers and treatment. In 2022, 42 percent of the world’s household wastewater was not safely treated (UN-Water, 2024). Every recovery on this page was paid for with public money, water bills or both; tell your representatives that you support it.
• Support farmers who protect water, and ask shops where their food comes from. Ask the brands you buy to publish how much plastic they sell in places without waste collection, and what they do to recover it.

When you travel

• Leave nothing behind. Take your rubbish home from beaches, rivers and lakes, especially where there is no regular collection.
• Refill rather than buy. Carry a refillable bottle and turn down single-use packaging and sachets; where tap water is not safe to drink, follow local health advice.
• Check before you swim, using the local water-quality signs or ratings, and stay out of the water after heavy rain in places with sewer overflows.
• Volunteer with care. If you want to help on a polluted river abroad, read go there, learn, and help below first.

Share your ideas

The rivers at the top of the ranking will not be fixed by one invention. They will be fixed by thousands of good ideas, tested where people live: a better bin route, a refill shop, a school club that measures its creek, a cheaper trap for a canal, a fairer price for collected plastic. Send us yours, as many as you have.

Go there, learn, and help

The most useful thing some people can do is to go. Engineers, nurses, teachers, designers, students and retired professionals can offer skills that are in short supply, and bring back an understanding that no article can give. If you are able to travel to one of these rivers, do it as a partner, not as a rescuer.

• Start by listening. Contact local organisations, universities, river councils and city offices before you arrive, and ask what they need. People living beside these rivers have been working on them for years.
• Work with governments and communities together. Lasting change needs both: local officials who can change collection routes and permits, and residents who decide what goes into the water every day. Offer to connect them, never to replace them.

• Teach, and be taught. Share what you know about monitoring, sanitation, waste systems or health, and learn how things really work there. Leave behind skills and open data, not dependence.
• Stay safe. Polluted water carries disease and chemicals. Follow your government’s travel advice, get the vaccinations a travel clinic recommends, never swim in or drink from these rivers, and respect local laws and customs.
• Keep it honest. The Local Solar System Foundation does not organise, sponsor or pay for travel. Anyone who helps does so as an independent volunteer and never collects money in our name.

When you come back, tell us what you learned through the form above, and consider starting a local chapter so that the work continues where you live too.

Sources and further reading

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• UN-Water, Progress on wastewater treatment, 2024 update
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• National Mission for Clean Ganga, Namami Gange programme
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