By FIONA MACRAE, Daily Mail

Last updated at 19:36 19 July 2006

A third of male fish in English rivers are changing sex due to 'gender-bending' pollution, alarming research shows.

Experts say female hormones from the contraceptive pill and HRT are being washed into our rivers and causing male fish to produce eggs.

The problem - which is country-wide - has raised fears that the pollutants could also be contaminating our drinking water - and even be affecting the fertility of men.

The Environment Agency study looked at the health of more than 1600 roach found in 51 rivers and streams around the country.

Overall, a third of the male fish were between sexes. However, in one waterway, near a particularly heavy discharge of treated sewage more than 80 per cent had female characteristics.

Tests showed the males developed female sex organs and were producing eggs. Such fish also produce less sperm and the sperm that is produced is of low quality. Females may also be affected, producing abnormal eggs.

Previous studies have that cod, trout and flounders are all being feminised.

Researcher Professor Charles Tyler said that the fish are swimming in a soup of oestrogen-like compounds, found in the Pill and in HRT.

The hormone, which is also produced naturally by women and found in industrial waste, is released into our waterways after surviving the sewage treatment process.

Prof Tyler, one of the country's leading authorities on the effects of oestrogen, said: 'There is a soup of oestrogen compounds, all with different degrees of potency and they are interactive in their effects - if you add them together, you add there are additional effects.

'This soup of oestrogen is responsible for causing these changes to the fish. It is abnormal. These fish should be male or female. The fact that we have got such a large proportion right across the country is not right.'

The Exeter University professor said it is too early to say what the long-term implications will be for Britain's fishlife.

While it may not initially have a big impact on stock levels, a reduction in the number of breeding males could lead to all sorts of genetic problems in later years.

'Effects like a change in how many males can contribute to the population can change the genetic structure of the population,' he said. 'In five years' item, the whole system could go belly-up.'

Human health could also be at risk, with oestrogen from contaminated food and water building up in our bodies.

Although there is no conclusive proof, it is thought the hormone, which has similar actions in fish and humans, could be partly to blame for falling sperm counts in men.

British men's sperm counts dropped by almost a third between 1989 and 2002, and one in six couples now have difficulty conceiving.

Prof Tyler said: 'There is certainly the potential for it to have an effect in humans - and possibly a marked effect.'

The Environment Agency is looking at ways of improving the sewage treatment process, to either remove oestrogen during the process or reduce the amount that is discharged into our waterways.