Worthing's sea water is cleaner now than it was 20 years ago.
The assurance was made by Councillor Peter Green, chairman of environmental health on the borough council, after the town failed two pollution tests last year.
Worthing will not be able to fly the coveted Blue Flag this year, a major blow to the town.
Responding to a question from the public gallery at a full council meeting, Coun Green said finding the source of the pollution was like looking for a needle in a haystack.
He said: "What contaminates the surface water outlets, and there are some 14 of these, we cannot tell. Our seawater is probably as good as those places that passed.
"It is just that we had one failure more. Therefore our water is not considered to be top quality but it is a lot cleaner now than it was 20 years ago."
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