Young women could be asked to avoid the contraceptive pill to save river fish populations, it was revealed today.

Top scientists from the Department of Health and Environment Agency have been discussing the effects of the hormones which find their way into rivers. While gender bending fish are a gift to tabloid headline writers, new research shows that the sustainability of some species could now be at risk.

Oestrogen finding its way into rivers, via sewage systems, causes some male fish to develop eggs instead of milt.

New research commissioned by the Environment Agency shows that up to a third of male fish in some rivers become infertile. Scientists at Exeter and Brunel universities came to the shocking conclusion after studying roach and gudgeon populations in 10 rivers, including the Nene and Aire.

At a London news conference Steve Killeen, Head of Chemicals Policy at the Environment Agency was asked if the Government would be asked to try and persuade young women to switch to other forms of contraception to save wild fish populations.

He told reporters: “The Agency has been looking at the whole issue of pharmaceuticals in the environment. Clearly any decision in relation to the use of the Pill is a fairly substantial question and it will go to the Government, whether it be the Department of Health or the Medicines Control Agency.

“The question is very valid and it is something we will discuss further.

“”It is part of the overall solution and if these materials are coming from people through natural systems or through synthetic materials such as the contraceptive Pill, it is part of a larger debate and a factor we will discuss with Government.”

Fears that oestrogen hormones, which end up in sewage effluent in rivers, were having this effect on male fish were first raised by research five years ago.