Disaster has been averted on a Fenland drain suffering from plummeting oxygen levels, the Environment Agency said today.
Emergency measures were put into place in the Delph, on the Norfolk/Cambridgeshire border, after anglers reported fish gasping for oxygen on the surface.
Officials said the problem had been caused by stale water which had been standing on Welney Washes all summer entering the river.
“We were concerned this could impact on water quality,” said EA senior environment officer Greg Oakes. “We were getting very low oxygen levels and we have an action plan for when levels fall.”
Aerators were installed to boost oxygen levels and supplies of hydrogen peroxide – which can be added to river water in extreme emergencies to provide a rapid oxygen boost – were placed at strategic points, as anglers and scientists expected a major fish kill.
But Mr Oakes said while a few had died in isolated pockets, the measures had largely worked.
“Oxygen levels have steadily gone up over the last few weeks at all key points,” he said.
“A lot of fish are carrying fungus, which is a sign of long-term stress, but we’ve not seen any major mortality – just small pockets.
“There is always an element of luck with all these things but we have spent large amounts of resource going up there nearly every day sampling.”
In recent weeks, pike anglers have noticed the water has an unusual dark tinge in several areas. The EA does not yet know what has caused it but does not believe it to be harmful to fish stocks.