Swimmers should avoid some 500 European beaches, lakes and rivers for health reasons, the European Commission said on Thursday after a survey of nearly 20,000 sites.
From the Atlantic to the Mediterranean, and the North Sea to the Black Sea, 96 percent of European Union coastal waters and 90 percent of lakes and rivers met minimum quality standards in 2009, the commission said.
A report published on Thursday analyses the results of tests conducted on 13,741 coastal and 6,867 inland swimming sites.
Delays in commissioning the monitoring program meant that 830 sites in Greece were not adequately monitored, the report's authors noted.
Online maps such as http://dataservice.eea.europa.eu/map/BathingWater/ give swimmers detailed information as to the state of beaches or waters they intend visiting.
France and Italy, which have far and away the greatest number of swimming sites at some 2,000 and 5,000 respectively, also have the highest number that failed tests.
France had the highest number of "non-compliant" sites 129, followed by Denmark (68), Italy (56), the Netherlands (46) and Poland (44).
Spain, which has almost as many sites as France, failed just 15, with 14 sites in Britain and 11 in Belgium also on the list.
The criteria stems from a 2006 EU law that sets bacterial guidelines on water quality.