Intensive agriculture and Britain’s increasingly wet climate are sending a cocktail of nitrates and other chemicals into our waterways. These cause a process called eutrophication, where waterways become coloured by algal blooms, which choke weed growth and sap oxygen from the water.

Now Nitrate Vulnerable Zones (NVZs) are being declared across approximately 50 per cent of rural England, which will limit the occasions when farmers can spread chemicals on their land.

Announcing the move at a London news conference, Environment Minister Michael Meacher said: “Great improvements have been made in reducing pollution from industrial discharges in recent years. But at the same time, agricultural production has become more intensive with the result that agriculture is now a major polluter of English rivers, lakes and coastal waters.

“We need to work closely with farmers to turn this problem around and achieve a cleaner and healthier environment.” He added.

More than 70% of the nitrates and 40% of phosphates in our rivers originate from farmland. And up to half of our coastal bathing waters suffer contamination by microbes from farm manure.

Officials at the Department of Environment, Food and Rural Affairs have also identified 32 stretches of river and coastal areas which are particularly at risk. These areas, which are predominantly in intensively-farmed East Anglia and include the rivers Yare and Ely Ouse, have been designated Nitrate Sensitive Areas, where even tighter controls will apply.

Water companies are also being ordered to cut phosphorous and nitrate levels in discharges from 53 sewage treatment works along these rivers and the Glen and Cam catchments.