Monitoring results to be unveiled by the Scottish Environment Protection Agency – Sepa – this week will name up to five of the nation’s official bathing waters as having breached 30-year-old sewage standards. This is the third year running that Scotland’s beaches have recorded poor results, with several having suffered repeated failures. As before, Sepa has blamed “exceptionally heavy rain” for flooding sewers and washing animal waste from farmland into the sea.

High levels of pollution in the water can give bathers severe stomach and ear infections, as well as skin rashes. In extreme cases, infections can be lethal.

The worst pollution has been at Ettrick Bay on the Isle of Bute, which Sepa regards as “disappointing” because of all the work that has been done to try and prevent run-off from local farms. The beach has failed to meet the legal limits in nine of the last 11 years.

The second confirmed failure for the summer has been at Sandyhills in Dumfries and Galloway. The bathing water there also failed in 2008 and 2007.

According to Sepa, three other beaches are “likely” to breach the sewage safety limits, although final results won’t be confirmed for a few days. They are Irvine, Heads of Ayr and Saltcoats, all on the Ayrshire coast.

“After a really encouraging start to the bathing water season from May to July, unfortunately August and early September have seen record rainfall in many places,” said Calum McPhail, Sepa’s environmental quality manager.

He pointed out that electronic signs had been installed by Sepa where ­pollution had been predicted. This was “a crucial component to allowing the public to make informed decisions,” he said.

The bathing season officially ends on Tuesday, and Sepa will confirm the final results after that. Seven beaches failed in 2008, and the same number in 2007.

The Marine Conservation ­Society highlighted the problems caused by sewers overflowing in heavy rain. “Once again, the story of the summer is of storm pollution leading to failures due to farm run-off, urban drainage and ­discharging sewer overflows,” said the society’s ­Scottish manager Calum Duncan.

He pointed out that there were hundreds of combined sewer overflow pipes around the Scottish coast, with some beaches having a dozen or more. When the weather turns bad, these pipes pour a mix of raw sewage and floodwater into the sea.

“Used judiciously, overflow pipes are a necessary fail-safe device for our sewers, but they are without doubt also causing bathing water pollution. In some cases, we believe that they have become a regular means of sewage disposal,” Duncan said.

He pointed out that the vast majority of the pipes were not monitored. “We would like to see the problem tackled with a systematic monitoring regime coupled with the expansion of Sepa’s highly successful bathing water quality forecasting system.”

Sepa revealed earlier in the summer that pollution at the Elie Harbour and Earslferry beach in Fife had caused it to lose its prestigious blue flag award for cleanliness.