But they have been unable to find a conclusive reason for the deaths and have blamed them on “poor oxygen levels” in the water.
Concerns began last week when members of the public noticed large numbers of fish floating in the stream that runs through Emerson Valley estate.
More dead fish were found in the lake, near the bandstand.
"It’s a horrible sight. There are hundreds of them just floating on the water. We have no idea why they died,” said a witness.
The matter was reported to The Parks Trust, which called in theEnvironment Agencyto conduct tests on the water quality.
The tests showed there were no pollutants that would have killed the fish.
A Parks Trust spokesman said: "We are aware of the dead fish in this area. This has been reported to the Environment Agency who have done tests on the water quality. They do not have any concerns in regard to pollution and believe the fish are dying due to poor oxygen levels in the water, which is known to happen on occasion.”
The spokesman added: “We will continue to monitor the area and liaise with the Environment Agency on this matter.”
In November 2020 there was a similar problem with huge numbers of dead fish found at Caldecotte Lake. Experts concluded the problem was cuased by heavy rainfall washing pollutants into the water.