Is it safe to swim in UK rivers? Sewage and water quality explained

Whether a river is clean enough to swim in depends on which stretch, and when. Some stretches of river are officially tested for swimmers through the summer. Rivers that aren't designated aren't routinely tested for swimmers. And rain changes the picture for every one of them. This guide covers how it works in England, with pointers for the rest of the UK.

Designated bathing waters

A designated bathing water is, in the Environment Agency's words, an officially recognised swimming spot: a beach, a lake or a stretch of river that's regularly tested and monitored for bacteria that can affect human health. There are 464 in England. Rivers are a recent addition. In 2020 the Environment Agency noted that no English rivers had yet been designated for bathing, and six of the 13 new bathing waters designated in 2026 are rivers.

From mid-May to the end of September, the Environment Agency runs more than 7,000 tests across these sites, looking for bacteria that indicate faecal contamination. The tests can't tell whether that contamination comes from people, through sewage, or from animals such as birds, dogs and farm livestock.

How the ratings work

Each designated water gets one of four classifications. Defra's statistics describe them like this:

• Excellent: the highest, cleanest class
• Good: generally good water quality
• Sufficient: meets the minimum standard
• Poor: has not met the minimum standard

A rating is based on samples from the last four bathing seasons, not one summer's results, tested for two bacteria, E. coli and intestinal enterococci, during a season that runs from 15 May to 30 September. In 2025, 417 of the 449 bathing waters assessed in England (92.9%) met at least the minimum standard, and 32 were rated Poor. Those figures cover beaches and lakes as well as rivers.

The rules changed in November 2025. A water rated Poor for five years in a row no longer loses its designation automatically; that's now a decision for ministers. Sites can also apply to change the dates of their bathing season.

A good rating still isn't a guarantee. As the Environment Agency puts it, "designation does not mean water quality will always be good." What designation gives you is reliable, up-to-date information about that water.

Storm overflows, and why rain matters

Combined sewers carry rainwater and waste water in the same pipe. The Environment Agency explains that storm overflows were developed as relief valves, to reduce the risk of sewage backing up when heavy rain pushes those pipes past their capacity. What overflows in heavy rain is diluted sewage.

Government policy says those discharges should only happen in exceptional circumstances, such as unusually heavy rainfall. All storm overflows now have monitors recording how often and for how long they operate, and since 1 January 2025 water and sewerage companies have had to publish their storm overflow data in near real time.

Sewage isn't the only source. The Environment Agency lists agriculture, urban drains and roads and highways among the others, and says pollution is more likely to get into rivers after rainfall. The Swim Healthy guidance from the Environment Agency and the UK Health Security Agency says heavy rain can wash harmful bacteria off farmland. Rain raises the risk even on a stretch with a good rating. Our guide to river swimming after rain covers what else changes when a river rises.

Rivers that aren't designated

If a stretch of river isn't designated, nobody is routinely testing it with swimmers in mind. The Environment Agency says non-designated waters aren't routinely monitored for bathing water quality, so they carry a greater level of uncertainty and risk. Swim Healthy explains why: those waters are managed to protect fish and wildlife, not people, so the health risks may be higher.

Canals are a separate case. The Canal & River Trust says it doesn't test its water but knows it isn't of swimming quality, and its advice is not to swim in its canals and rivers. More in locks, gates and bridges.

How to check before you go

• On Wild, spot pages show the official bathing-water rating where a spot is a designated bathing water. River spot pages also show recent rainfall and the river level.
• For designated waters in England, the Environment Agency's Swimfo service shows each site's classification and monitoring results, and at a number of sites it issues daily pollution risk forecasts that flag when rain, wind or high tides may temporarily affect water quality. For Scotland, Wales and Northern Ireland, Swimfo points you to SEPA, Natural Resources Wales and DAERA.
• Water companies publish storm overflow data in near real time.
• After heavy rain, the Environment Agency's advice on reducing risk includes not swimming after recent rainfall.

When you do swim

The Swim Healthy advice: before you go in, cover any cuts with a waterproof plaster. While you swim, try not to swallow the water or splash it into your mouth. Afterwards, clean your hands thoroughly with soap and water, especially before eating.

If you become unwell with diarrhoea or other symptoms, seek medical help and tell them you've been open water swimming. Swim Healthy says not to swim again until you've had no diarrhoea for at least 48 hours, or longer if your doctor advises.

Water quality is one part of a river swim. The river swimming guide covers the rest, and the general safety checklist covers every swim, whatever the water.

Sources

1. Environment Agency, Helping you choose where and when to swim in open water
2. Department for Environment, Food & Rural Affairs, 2025 Statistics on English coastal and inland bathing waters: A summary of compliance with the Bathing Water (Amendment) (England and Wales) Regulations 2025
3. Department for Environment, Food & Rural Affairs, 87% of bathing waters rated 'Excellent' or 'Good' as new reforms come into law
4. Environment Agency, Combined Sewer Overflows Explained
5. Department for Environment, Food & Rural Affairs, Storm overflows: policy and guidance
6. Environment Agency and UK Health Security Agency, Swim healthy
7. Environment Agency, Swimfo: Find a bathing water
8. Canal & River Trust, Summer water safety

This guide is general information, not a substitute for local knowledge or training. Conditions change: check them on the day, and if in doubt, don't go in. Images on the blog are illustrations, not pictures of specific spots.