The bathing water at 63% of the UK's beaches tested in a survey has been awarded a rating of "excellent".
Blackpool beach achieved a Basic Pass in the MSC's survey
The top rating was given to 494 out of 787 beaches checked by the Marine Conservation Society on the 20th anniversary of its Good Beach Guide.
But the MCS warned global warming might cause water quality to fall in future.
The Blue Flag awards, which are given to the cleanest beaches in England, have also been announced, with 85 beaches winning this particular prize.
Thomas Bell, the MCS's coastal pollution officer, said: "MCS is delighted to recommend over 60% of UK beaches this year on the basis of excellent water quality.
"This is great news for the thousands of holidaymakers heading to the British coast this summer.
"We're also delighted to report that the number of beaches achieving our tough water quality standard is four times higher than 10 years ago.
MCS BEACH AWARDS
South West of England - 156 recommended out of 195 beaches monitored
South East - 98 recommended out of 135
North West - 7 recommended out of 33
North East - 52 recommended out of 67
Scotland - 48 recommended out of 110
Wales - 104 recommended out of 175
Northern Ireland - 13 recommended out of 27
"Britain's beaches used to be awash with sewage, and the Good Beach Guide drew a line in the sand 20 years ago for what was acceptable.
"Today we're enjoying the benefits of that campaign."
But the MCS said the number of beaches achieving the top water quality standard may have peaked because storm-related pollution, a result of climate change, has become an increased threat to coastal waters.
Low rainfall, such as that experienced in three of the last four British summers, boosts bathing water quality because of a lack of storm-related pollution.
Warmer, wetter winters and summers which contain violent storms and flash floods are forecast to be a consequence of climate change and the MCS says these will substantially increase coastal pollution pressures.
Mr Bell said: "Heavy rain translates into poor weather quality because waterborne pollutants such as raw sewage, petro-chemicals and farm waste by-pass the sewer system and sweep directly from the land into rivers and the sea.
"This effect was particularly apparent across the UK during summer 2004 and throughout last winter.
"It's a serious problem that we believe will worsen in years to come."
Alan Woods, chief executive of ENCAMS, which runs Blue Flag in England, said the winning beaches in its survey were a sign of a "fantastic achievement".
He said: "Beaches put up for a Blue Flag face three rounds of judging, the final being the international jury.
"Standards are high and there is little leeway for those that make the cut.
"That's why any beach bestowed a Blue Flag should be shouting from the rafters celebrating such a fantastic achievement."
The Blue Flag survey, which is conducted worldwide, measures 29 criteria from accessibility for disabled visitors through to the number of bins provided, lifeguards and litter levels.