What are the UK's main sources of poor river water quality?

What are the UK's main sources of poor river water quality?

The UK's rivers are polluted by a combination of sewage, agricultural runoff, urban drainage, industrial discharges and historical contamination. The relative importance of each source varies between catchments, but sewage pollution and agricultural pollution are two of the most significant and widely discussed pressures on river water quality.

Pollution doesn't just make water look dirty. It can reduce dissolved oxygen, encourage excessive algal growth, damage aquatic insects and fish, contaminate drinking-water sources and make rivers less safe for recreation.

The six main sources of river pollution

1. Sewage and wastewater discharges

Major pressure

• Storm overflows releasing untreated sewage mixed with rainwater.

• Treated wastewater containing residual nutrients, chemicals and organic matter.

• Failures or bypasses at sewage treatment works.

• Leaking or misconnected sewers.

Main impacts: faecal bacteria, ammonia, phosphorus, oxygen depletion, pathogens and risks to human health.

2. Agricultural pollution

Major pressure

• Fertiliser and manure washed from fields.

• Livestock slurry entering watercourses.

• Cattle accessing riverbanks and depositing faeces directly into rivers.

• Soil erosion and sediment runoff.

• Pesticides and other agricultural chemicals.

Main impacts: elevated nitrates and phosphates, algal blooms, cloudy water, habitat damage and oxygen depletion.

3. Urban runoff and road drainage

• Rainwater washing oil, fuel residues, tyre and brake particles, metals and litter into drains.

• Road and construction-site sediment entering streams.

• Contaminated runoff from industrial estates and paved surfaces.

Main impacts: toxic substances, microplastics, sediment pollution and sudden pollution pulses during rainfall.

4. Industrial discharges and contaminated land

• Effluent from factories and industrial processes.

• Metals, solvents, process chemicals and other hazardous substances.

• Leachate from contaminated land and some landfill sites.

• Pollution from historic mining and industrial workings.

Main impacts: toxic effects on aquatic organisms, chemical contamination of sediments and persistent pollution that can remain for decades.

5. Soil erosion, sediment and construction

• Bare soil exposed by ploughing, earthworks and construction.

• Runoff from forestry operations and poorly protected riverbanks.

• Fine sediment entering rivers after heavy rain.

Main impacts: smothered fish eggs, clogged gravel beds, reduced light penetration and damage to the habitats of aquatic insect.

6. Other pollutants and low river flows

• Pharmaceuticals, PFAS and other persistent chemicals.

• Microplastics and household chemicals.

• Abstraction and drought reducing dilution.

• Warmer water and low oxygen levels during hot weather.

Main impacts: chronic chemical exposure, greater concentration of some pollutants, ecological stress and increased vulnerability to other pollution sources.

Using Evidence to Rank Pollution Sources

The Environment Agency's national evidence for England identifies agriculture, the water industry and urban/transport runoff as major pressures on rivers. Its 2024 summary reported the following proportions of water bodies affected by these sources.

A key distinction is that the water industry figure covers wastewater pressures as a whole, including sewage treatment works and storm overflows. Storm overflows alone were identified as the reason for failure in 7% of water bodies in the Environment Agency's 2024–25 reporting.

Why river pollution is difficult to solve

• Multiple sources combine: a river may receive treated sewage, farm runoff and road drainage within the same stretch.

• Rainfall can trigger pollution: heavy rain washes nutrients and soil from fields and streets and can trigger storm overflow discharges.

• Pollution can be invisible: dissolved nutrients, pesticides, metals and PFAS may be present even when the water looks clear.

• Physical damage matters too: barriers, modified channels, excessive abstraction and loss of natural habitat can harm river ecology even without a direct pollution discharge.

• Legacy pollution persists: abandoned mines and contaminated sediments can continue releasing metals long after the original activity has ceased.

Where can you find the official data?

The Environment Agency's Catchment Data Explorer allows you to investigate individual rivers, their ecological status and the identified reasons for failing to achieve good status. The data can help distinguish between agricultural pollution, wastewater, urban runoff and other pressures.

For a local assessment, it is important to distinguish chemical status, ecological status and bathing-water quality: each measures different aspects of water qualit