Members of the public are being asked not to swim at Balbriggan Beach on Dublin's northside.
Fingal County Council has put a temporary 'Do Not Swim' notice in place.
It is due to an overflow at Quay Street Pumping Station in Balbriggan, which happened as a result of yesterday's heavy rain.
Fingal County Council spokesperson Gerry McDermott hopes tests on bathing water samples will lead to the ban being lifted.
He said: "The prohibition notice is precautionary, pending the outcome of laboratory analysis on bathing water samples which are scheduled for early next week.
"if the results are clear, it's hoped that the beach can reopen for bathing."