BE careful where you swim.

Some of Scotland's bathing waters are still contaminated with dangerously high levels of sewage, in breach of a European law introduced nearly 30 years ago.

The latest monitoring results reveal that, just halfway through the summer, three official bathing waters have already failed the basic sewage safety limits. They are Nairn East in Highland, Stonehaven in Aberdeenshire and Eyemouth in the Borders.

Another three are at risk of failing: Ettrick Bay on the Isle of Bute, Carrick Bay near Gatehouse of Fleet, and Peterhead Lido. In 2004, four of the official bathing waters failed, compared with three in 2003.

A further two popular beaches, which have not been formally designated as bathing waters by the Scottish Executive, have also been badly contaminated with sewage.

They are Stevenston in North Ayrshire and Helensburgh in Argyll and Bute.

"It is unacceptable that almost 30 years after European laws on clean bathing water were written, Scottish beaches are still failing, " said Dr Richard Dixon, director of the environmental group WWF Scotland.

"It is particularly galling that 2005 is looking like it will end up being as bad as, or worse than, 2004."

The climate change being caused by pollution will increase the growth of sewage bacteria, he argued, so greater efforts will be needed to solve the problem in the future.

Some 60 designated bathing waters, along with 46 undesignated beaches, are sampled 20 times between June and September by the government watchdog, the Scottish Environment Protection Agency (Sepa).

Faecal pollution of the water can cause serious illnesses, including stomach upsets, diarrhoea, ear infections or worse. The contamination can come from untreated human sewage, or from animal waste washed from the land by rain.

"We are disappointed that halfway into the summer the water quality at three beaches has failed for the season, " said a spokeswoman for Sepa.

"These have all been at times of heavy rainfall."

The spokeswoman pointed out, however, that the majority of bathing waters were within the safety limits.

"There are many good quality beaches across Scotland and people should continue to enjoy all that they have to offer, " she said.

At Nairn East, Sepa blamed "discharges from sewer overflows" for increasing bacteria levels in the River Nairn, which runs into the bathing water.

At Stonehaven, Sepa pointed out that sewage improvement works had been delayed by a public inquiry. Meanwhile, the breach of the safety limit at Eyemouth has been attributed to "excess bacteria levels" in the Eye Water, though investigations are continuing.

The failures at these three beaches have come as a surprise since none of them has failed in the last four years.

"These mid-season sample failures are particularly disappointing for Nairn and Eyemouth, where sewage is subject to tertiary and secondary treatment, " said Calum Duncan, the Scottish officer for the Marine Conservation Society. "If bacterial contamination from the rivers Nairn and Eye were to blame, with wet weather also increasing the bacterial load from farm run-off at Eyemouth, it is imperative that sewage sources affecting these rivers are located and remedied, " Although the quality of bathing water had improved in recent years, there were still 58 beaches in Scotland that suffered from inadequately treated sewage, Duncan claimed.

According to Scottish Water, the failure at Stonehaven highlighted the need for a planned pounds-10 million investment in sewage treatment. It was "disappointing" that this was now unlikely to be in place in December because of public opposition, said the government company's communications director, Atholl Duncan.

"With Nairn and Eyemouth, the rivers may have contributed to the failures, " he continued. "We are in the midst of investing pounds-2.2m to upgrade the Nairn works and tackle four discharge points to the River Nairn."

The Scottish Executive emphasised that the state of Scotland's bathing waters had greatly improved.

"In 1990, only half our waters passed mandatory quality standards, but in 2004 93-per cent passed, " said a spokeswoman.

"We recognise that more needs to be done. That is why we have invested pounds-1.6 billion since 2000 in Scotland's water infrastructure."