Dangers in a dip

Some of London's most popular swimming pools are so dirty that they pose a threat to health, an Evening Standard investigation can reveal.

Tests have shown that bacteria including E.coli from human faeces is regularly present in outdoor pools.

Levels are sometimes so high microbiologists warn that, if the water was swallowed, it could cause vomiting and diarrhoea.

The Evening Standard visited nine swimming pools at the start of this week as the heatwave hit its peak.

A sterilised test tube was filled with pool water and delivered to an internationally renowned laboratory for a series of detailed microbiological tests.

The results showed that the quality of the water at four of the pools was poor. Three of them - Brockwell Park Lido, Oasis Sport Centre and the Serpentine Lido - contain such high levels of bacteria, called coliforms, that experts believe the water is of serious concern.

Brockwell Park Lido - nicknamed the Brixton Beach - attracts thousands of people during hot weather. But the 50-metre pool, which costs £5 to use, was found to have high levels of bacteria including E.coli. The general quality of water was also poor.

A sample from the Oasis Swimming Pool and Sports Centre in Holborn was found to contain similar levels of bacteria.

According to health guidelines, such results suggest that "there is likely to be a serious defect in the pool operating system, such as failure of the disinfection process and/or a problem with the chemical balance of the pool or the filtration system, which will require immediate attention".

Hampstead Heath Bathing Pools and the Serpentine Lido were also found to contain E.coli and other bacteria. However, as both pools are part of outdoor natural ponds complete with ducks, this is perhaps less surprising.

The microbiologist who performed the tests said the fact five pools tested had reasonable or good quality water with little sign of bacteria meant that keeping pools clean was not impossible.

"When you find bacteria such as E.coli it suggests other organisms such as salmonella could also be in there. It is those things which can make you ill if you swallow the water," he said.

"When you have lots of children in a pool you will get E.coli from faeces but chemicals should eradicate these. But in some cases this appears not to be happening."

Today a Brockwell Lido spokesperson said it had had an extremely busy weekend and the pool was not cleaned until Monday. It was now "crystal clear".

Hampstead Heath Ponds said the findings were as expected for a natural water pond. "That is why people come every day - because it's natural without chlorine and with ducks," a spokesman said.

The Oasis Swimming Pool was unavailable for comment.

Despite the findings, microbiologists point out that swimming in the sea exposes people to greater levels of E.coli.