Staithes, North Yorkshire, is the only beach in the country to have been rated "poor" by the Environment Agency (EA) so far this year.
EA inspectors take weekly water samples at 494 sites to measure pollution levels between May and September each year.
Tests have revealed that water quality in 97 per cent of bathing sites in England and Wales is good enough to be classified as "excellent", compared with only 76 per cent 10 years ago.
The agency said recent good weather, action to reduce pollution from farms and tighter regulation of sewer overflows were responsible for the results.
Chris Tuckett, who leads the agency's work on bathing waters, said: "We'll be working with surfers, swimmers, farmers and water companies to ensure the quality of our bathing water continues improving."
Last week, the Marine Conservation Society warned that about one beach in seven was likely to fail tough new EU standards.