Over half the UK's beaches are recommended for having excellent water quality in the latest Good Beach Guide - a slight rise on last year, the Marine Conservation Society has said.
The number of sites failing the MCS's latest bathing water tests, which are based on European standards, fell from 66 in the previous guide to 41 this year.
But around one in seven beaches, including tourist hotspots such as Rock in Cornwall, Weston-super-Mare's main beach and Robin Hood's Bay in North Yorkshire - are likely to fail tougher new EU standards being introduced in 2015, the MCS warned.
This year 421 bathing spots (55%) were given the thumbs up in the guide, an improvement on 388 (50%) last year.
But the conservation group said the latest tests, carried out from May to September 2009, showed the water quality of UK beaches had not returned to the record highs of 2006 because of extremely wet summers since then.
Higher seasonal rainfall causes a network of sewer overflows to discharge raw sewage on to some beaches from an overloaded system, the MCS said.
The high level of rain also washes pollutants such as animal waste, fertilisers and rubbish from farmland and cities into rivers and to the sea.
The MCS is also concerned that more beaches will fail the water quality tests when stricter European levels are introduced in 2015.
The society only recommends beaches if they exceed the existing higher "guideline" EC water quality standards and are not affected by inadequately treated continuous sewage discharge.
More than 80 beaches around England and Wales will fail to meet even minimum water quality standards under the more stringent EU regime without action to improve them now, the society warned.