A two-mile stretch of the Old Bedford River at Welney has been affected, with the water losing most of its oxygen.

Thousands of fresh water fish, including roach, perch and bream, died as a result of low oxygen levels in the water.

The fish were removed from the water by Environment Agency officials and buried in a nearby landfill site.

'Biological quality'

Aerators have now been set up along the riverbanks to mechanically pump oxygen back into the river for surviving fish.

A spokesman for the Environment Agency said the incident was one of the worst of its type in East Anglia.

Pollution was believed to have caused the drop in oxygen levels in the river, but experts now believe it may have been caused by an excess of algae.

Kevin Rutterford, environment protection manager for the Welney area, said: "The cause of the low oxygen levels has not been established but there are no factories or big sewage treatment works discharging into the river.

"So we are focusing our efforts on the biological quality of the river. We are specifically looking at the algal content of the river."

He said tests had been carried out and until the results were known, they were "keeping their option open."

Mr Rutterford said fish still remained in parts of the river and the water quality was being monitored constantly.