If you're heading to a beach this bank holiday it's a good idea to make sure the water is clean enough to swim in.
The Marine Conservation Society says the sea water at British beaches has got dirtier in the past 12 months.
The MCS says the wet summer in 2008 washed a lot of dirt and chemicals into UK rivers and seas, and that means more beaches aren't safe to swim at.
The MCS tested sea water at every UK beach, and for the first time say fewer than half of them are clean enough.
Of the 777 beaches in the UK the Marine Conservation Society reckons that only 370 of them have water clean enough to recommend.
Beaches in Scotland, Northern Ireland and north west England are apparently the worst.
A spokesperson for the MCS said that in order to avoid health risks, people should pick places to swim in the sea which had a good water quality record.
He added you should stay out of the water for at least 24 hours after heavy storms and report pollution problems to the MCS.