The fish have been spotted washed up on the banks of Worthington Lakes.
Owners United Utilities have placed notices up asking people not to remove sick fish from the lake so that they can be sent away for testing.

The utility giant has also reassured people that the drinking water supply has not been contaminated and there is no risk to the public.

The Environment Agency has now been called in to investigate but it is understood that water tests carried out by UU have not shown anything suspicious, although fishing has been suspended on all three lakes. All the fish are believed to be "elderly" carp.

A United Utility spokesman said: "We have notified the Environment Agency who have taken some dead fish away for examination. Between 50 and 60 fish have died but the cause is a mystery. They have all been elderly carp.

"The water is tested on a regular basis and there are no problems there."

An Environment Agency spokesman said: "We have visited the site and taken two fish away for investigation. At this point we don't know why they have died.

"The investigation is a lengthy process as we carry out different tests for viruses and parasites. We should have the results back by mid-May."
Carp are susceptible to a wide variety of diseases including the deadly Koi Herpes virus which is becoming an increasing problem across the country.

Restrictions, including disinfection for net dipping and boots, were introduced after a confirmed outbreak in Abram last summer at Kingsdown Flash.

Secretary of Warrington Anglers' Association, which has the fishing lease for Worthington Lakes from owners UU, Frank Lythgoe said: "It is not uncommon for fish deaths to occur at this time of year.

"We will have to wait until the Environment Agency has concluded its investigation before we come to any conclusions.
"From the fish I noticed down there they were small, younger fish that had died."

But John Weedon , of the Lancashire Fisheries Consultative Committee and angling writer said: "KHV is becoming a major problem across the country. It takes between 20% and 90% of carp stock and it has been found in the Wigan area within the last year."