Very heavy seas and gale force winds have been blamed for the worst water quality result seen at Broughty Ferry beach for many years.
Experts from the Scottish Environment Protection Agency were initially baffled by the result of a September 6 test, which showed the number of bacteria recorded in a sample was many times higher than the level permitted by the set criteria.
As such the beach recorded its first “fail” of the bathing season, unable to reach the mandatory minimum standard recognised by testers.
But SEPA investigations have revealed that unusually high seas and strong winds were responsible for the lack of cleanliness.
A spokeswoman for the agency said that the conditions had been blamed for similar failures on beaches in Fife at the same time.
The bathing beach has had a poor season, and seems unlikely to retain its Blue Flag status into 2011.
An annual programme of testing to guarantee standards found the beach had failed to reach the top “guideline” water quality mark on six occasions and a further test had to be discounted due to abnormal weather.
Four is normally the maximum number of slips permitted but Keep Scotland Beautiful, which administers the Blue Flag scheme, has offered the beach a glimmer of hope, saying it would wait until all the results were in before taking a final decision.