Rivers, including the Test and the Itchen, could be damaged forever unless urgent action is taken.

The first report on the state of England's 161 chalk rivers was launched in Winchester yesterday.

Chalk rivers, of which Hampshire's Test and Itchen are two of the most famous and pristine, form a valuable and irreplaceable part of our national heritage.

But they face mounting man-made threats which groups including the environment Agency and English Nature say must be tackled.

Sir John Harman, chairman of the Environment Agency, said this week: "The Test and the Itchen are as much part of our national heritage as Winchester Cathedral or the Houses of Parliament.

"The Itchen is in very good condition, but it is not universal. Some areas further downstream are affected by emissions. The Test is patchy because it is a long river and the problems increase the nearer the sea you get.

"The report is not a clean bill of health, but not a verdict of death, either. It's saying: 'Here are the issues and we want people to understand what they are so they can be tackled'."

The crystal-clear rivers support a diverse range of rare and endangered species and provide water for drinking, industry and agriculture. Rivers such as the Test and Itchen are also world-famous for fly-fishing and offer popular walking routes.

But they are fragile ecosystems facing growing threats, including urban and infrastructure developments, agriculture, effluent discharges, land drainage and flood defences.

Speaking at the launch at the Cathedral Refectory, Sir John added: "Chalk rivers, apart from being this habitat of huge national and international importance, are a barometer of our natural environment, of how usefully we are using or abusing natural resources."

The UK Biodiversity Action Plan Steering Group for Chalk Rivers produced the new report to set out how the rivers can be preserved.

Half of the sites surveyed for the report are of high or very high quality, nearly one third are poor, or very poor.

The report found that while water crowfoot and otters were recovering, stocks of salmon remained seriously low and decreasing fly life has been reported. Species such as the water vole and white-clawed crayfish were also under threat.

To make their vision a reality, the experts say they need to maintain and enhance the habitats of chalk rivers and their inhabitants, restore water quality, flows and habitat diversity and identify costeffective means of restoring damaged river reaches.