The health risks of swimming in UK rivers

“The most dangerous pathogen found in our rivers is E. coli which, if ingested, can cause chronic diarrhoea and vomiting and can, in rare cases, kill you. If you have an injury, you could get sepsis from it,” says Charles Watson, the founder of River Action UK.

“With the high levels of rainfall, huge quantities of raw sewage have been pouring out from our water companies directly into rivers. The combined sewage system in the UK means the pipe that takes the drain water away is the same pipe that takes the sewage out of your toilet, and because most sewage works become overwhelmed by rainfall very quickly, they have to open the combined storm overflow pipe, releasing sewage into our waterways.”

River Action UK’s E. coli testing of the waters between Hammersmith bridge and Putney in the run-up to the Oxford Cambridge boat race gave average E. coli levels of 10 times above what they should be for safe bathing, causing illness among the Oxford crew.

Regular testing of water at the newly designated bathing sites may be a move in the right direction but, warns Wardley, current testing may be inadequate. “There’s a certain amount of evidence that we should also be monitoring things like norovirus, rather than relying on E. coli bacteria, which are everywhere in the environment and not necessarily the best indicator of risks to human health.” 

How to know if your local river is polluted

The Rivers Trust has produced an active map that shows where the sewage network discharges treated effluent and overflows of untreated effluent and storm water into rivers. It means you can identify and avoid entering water that’s immediately downstream of these discharges and avoid the overflows, especially after it has been raining.

“Water companies’ live monitors on their websites show where they are discharging sewage at a particular time, but it’s not just what is being discharged that is of concern, but what is already in the river,” says Watson.

When sewage goes into the river, it settles as sediment and permeates into the vegetation and incubates as a pathogen. “Bacteria and algae love heat and as temperatures rise, this pathogen is accumulating in the rivers,” notes Watson. “And without public health advice from the Government, it’s hard to know whether this makes it unsafe to swim there.” 

“No river water is going to be clean enough to consume, but understanding water quality in rivers will help you identify when it isn’t OK to plunge in,” cautions Foote. “If water doesn’t smell right, it probably isn’t right. If there is scum or a film on the water, or a high level of weed and algae, it won’t be clean enough for a swim – nor enjoyable.”

If you do detect wildlife nearby, however, that’s a more positive sign. “Birds, fish, plants and insects don’t like dirty water,” says Foote, “so if you spot any, you’re in safe company.”

Algae blooms, by contrast, are bad news. According to Foote, large areas of dense floating weed and green murky water can indicate high levels of nitrates, phosphates and toxins. Blue-green algae can be toxic if swallowed, can cause skin rashes and be fatal to dogs. “It is easy to spot and often smells bad – you can taste it in the air – and it looks green and scummy,” says Foote.

Measures to take when swimming in rivers