Last Saturday saw distress calls raised by anglers near Winsford, Cheshire, when fish were noted as gasping and in distress.
Resulting tests in the water revealed depleted oxygen levels, although PFK is unable at this time to find exactly what those levels were.
To help alleviate the problem, oxygen is being added to the river, including through the use of hydrogen peroxide.
Tom Thornett from the Environmental agency adds: "Hydrogen peroxide is used to increase oxygen levels in the water and, in this case, may have created a build-up of foam because of reaction with small traces of detergent found in the water."
The search is still on to find what caused the depletion, but it is suspected that naturally occurring algae has played a key role in stripping oxygen from the water.
In the event, it is known that at least six different species of fish have been adversely affected, including tench, perch and carp.
It’s not known how many fish have died, although Steve Beech of Winsford and District Angling Association hints that figures may be as high as tens of thousands, thought this has not been verified. He goes on to say that the impact of the fatalities will have ramifications over many years.
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