People are being advised not to swim at 24 beaches in Devon and Cornwall because of bacterial pollution.
The Environment Agency blamed heavy rain for the problem, “as we have seen over the last couple of days”.
It said the pollution was “short term” and did not expect it to last more than 72 hours.
Beaches affected include North Sands in Salcombe and Goodrington near Paignton, both in Devon, as well as Summerleaze in Bude, Cornwall, said the agency.
An agency spokesperson said there were a “number of factors that can influence the quality of bathing waters”, including wind, sunlight, rain and tide.