Heavy storms this summer have threatened to pollute Britain's bathing beaches, a watchdog has warned.
Untreated sewage flows into the sea near many beaches after storms
The Marine Conservation Society wants signs put on beaches to warn swimmers that they could face health risks if they swim shortly after heavy rain.
Many UK beaches have sewer overflows on or near them, which divert untreated sewage into the sea following storms.
But the Environment Agency said it was "not identified as a major problem" and that beaches were "cleaner than ever".
The Marine Conservation Society (MCS) warning came after sudden downpours this summer wreaked havoc in different parts of Britain.
As well as the flood which devastated the Cornish village of Boscastle, and the landslide in Scotland which trapped motorists on a road below, a number of rivers have burst their banks.
After one heavy downpour in London earlier this month, 50,000 tonnes of raw sewage flowed into the Thames when sewers were unable to cope.
After another influx of sewage into the river, thousands of fish suffocated.
Hepatitis A 'risk'
The MCS fears problems around Britain's coastline where many beaches are adjacent to sewer overflows.
"What we are talking about are not serious problems, but fairly short-lived illnesses such as gastroenteritis and eye and ear infections," Thomas Bell of the Marine Conservation Society told BBC News Online.
Boscastle in Cornwall has been badly affected by recent flooding
"We are not saying people will get them, simply that the chances of getting them rise after rainstorms.
"We would ask swimmers to avoid going in the sea for a day or two after heavy rain."
The World Health Organisation says evidence linking sewage pollution to diseases such as hepatitis A, enteric fever, polio and typhoid is inconclusive, but may be proven after sufficient clinical research.
How long the sewage takes to disperse depends on whether the coastline is exposed, in which case it will be quick, or very sheltered, when it will be slower.
The other potential risk after flooding is associated with what is known as "diffuse pollution".
This is caused by pesticides, fertilisers or other substances washing off the land into the sea and can affect any beach, even if it does not have a sewage outlet.
"The MCS recognises that Combined Sewer Overflows (CSO) are necessary to avoid sewage flooding roads or people's houses, and that diffuse pollution is an entrenched and difficult problem," Mr Bell said.
"However, bathers are put at risk because beaches with normally excellent water quality, some possibly recommended in the MCS Good Beach Guide, can be temporarily affected by CSO discharges and or diffuse pollution, and many people may enter the sea in ignorance of this fact."
At present there are limited beach signage schemes around parts of the UK.
"We are urging the government and beach managers to adopt a mandatory national scheme to provide permanent public information about storm pollution on every bathing beach," said Mr Bell.
An Environment Agency spokeswoman said: "We are working with water companies on their environmental programmes, to improve sewage systems. It hasn't stopped the discharges from the CSOs completely, but it has reduced the problem significantly.
"We will continue to push for water companies to upgrade and improve sewage systems, so that we see fewer and fewer cases in freak storms of them having to use the CSOs and sewage going into our waters."
She added: "We monitor beaches in all types of weather, all the year round, and the results show that we have beaches that are cleaner than ever."