A water quality test taken close to a European Blue Flag beach in south Devon was more than 20 times over the pollution standards limit.
Torbay Council said animals could have produced a rogue result
The Environment Agency tested the water near Meadfoot Beach in Torquay.
When a sample of sea water contains more than 2,000 colonies of faecal coliforms, which is sewage bacteria, the water fails. The test near Meadfoot contained 55,000.
Torbay Council said when it got the result, officers immediately inspected the beach and spoke to local divers and workers who were not aware there was a problem.
The council said the reading may have been misrepresentative because a seagull or dog dropping near where the sample was taken may have caused the unusually high result.
Mike Yeo of Torbay Council said: "It's very difficult to be specific as to what it might have been.
"But there was no sign of any problem down there when we went and visited the site."
Another test was taken and the water was passed as safe.
Last week, red flags were put up on Dawlish Town Beach by Teignbridge District Council because it had a test that failed. But in that case, the result was only just over.
The beach was re-opened a day later.
Rich Hardy from the campaign group Surfers Against Sewage said the public should be better informed when standards fall.
He said: "I think a system has to be out into place at European Union level and I think we're going some way now to seeing that.
"I think the incidents over the summer in this area have highlighted the need for that.
"At the moment, it's down to local authorities themselves to make those decisions.
"We'd like to see more local authorities endorse the action of Teignbridge taken on that day."