The quality of Britain's coastline has fallen for the first time in eight years, an annual study warned today.
Researchers compiling this year's Good Beach Guide said the number of beaches failing European water quality tests has doubled since 2003.
The Marine Conservation Society (MSC) said 52 beaches failed tests last summer – up from 26 in the previous year – and confirmed the number of beaches it recommends as safe has also dropped.
Spokesman Thomas Bell said increased pollution was the result of wet weather last summer, which washed more detritus into the sea.
"The Met Office issued 100 flash weather warnings in August alone, and big storms produce poor water quality," said Mr Bell.
His findings come a day after the European Commission praised the UK for meeting EU standards for clean bathing water – with pass rates of 97.7 per cent for coastal water and 100 per cent for the 11 freshwater lakes tested.
However, the MSC said it "wouldn't advise" swimming at beaches which have failed water quality tests and claimed swimmers who do put themselves at risk of infections such as gastroenteritis.
The guide recommends a total of 427 stretches of sand from the 800 across the UK monitored for water quality, down from 453 last year.
A spokesman confirmed it is the first time the number of recommended beaches has fallen since 1997.
The guide reveals quality differences across the regions of the UK – with a total of 75 per cent of monitored beaches in the South West recommended – the highest for the region.
However, Scotland has seen its recommended beaches fall from 56 to 50.
The results of the EU standards tests published yesterday found that only 13 out of 562 seaside resort beaches failed to meet safety requirements.
The society said the guide is one of four beach monitoring schemes and the only scheme to focuses entirely on water quality standards and the risk of sewage pollution.
Mr Bell said: "MCS is urging the Government and Scottish Executive to provide better public information on all bathing beaches, advising swimmers that heavy rain can temporarily increase levels of bacterial pollution in the sea, with a consequent risk to bathers' health."