The Marine Conservation Society recommended just 370 out of 775 of the UK’s most popular bathing beaches in its annual Good Beach Guide, a fall of 17 per cent on last year and the lowest number since 2002.
Swimmers were advised to use a further 327 beaches only at certain times of year.
Beaches failing the minimum legal standard for swimming jumped almost 50 per cent this year, from 53 to 78. Popular beaches to fail the test included Plymouth Hoe West in Devon, Seaton Sluice in North Tyneside and Morfa Bychan in Wales.
Thomas Bell, MCS coastal pollution officer, blamed the fall in water quality on the heavy rain last summer which increased pollution in the rivers and the seas.
The latest bathing water tests were carried out between May and September 2008, coinciding with the seventh wettest British summer on record.
“Today’s results reflect last summer’s heavy rain which swept waterborne pollutants like raw sewage, petro-chemicals and farm waste into rivers and the sea,” he said.
“MCS is now recommending 25 per cent fewer beaches than three years ago and we’re becoming concerned that the existing infrastructure for handling storm pollution may not be up to the job.”
Mr Bell added that in order to avoid health risks, people should pick places to swim in the sea which had a good water quality record, stay out of the water for at least 24 hours after heavy storms and report pollution problems to the MCS.
The organisation said it believed specific counter pollution measures, including investment in more sustainable urban drainage systems, new farming practices and expansion of the sewer system to handle storm water, was necessary in the face of changing weather patterns brought on by climate change.
Earlier in the year the MCS found record levels of litter on Britain’s beaches with some 385,659 items of rubbish including plastic bags, sanitary items, fishing nets, cigarette butts and cotton bud sticks picked up by volunteers.
Keep Britain Tidy have also reported the number of beaches awarded a Blue Flag for overall cleanliness this year fell by 11 to 71 – although that is still an improvement from 2002 when just 45 made the grade.
The Department for the Environment has in place a number of ongoing programmes to reduce water pollution and deal with heavy rainfall.