Thousands of fish have died after oxygen levels in the water crashed to low levels.
A reader contacted the Northamptonshire Telegraph after seeing dozens of dead fish piled up on the bank by Kinewell Lake last week.
The dead fish found at the lake in Ringstead include roach, bream and some carp.
A spokesman for the Environment Agency, which has been out to investigate the problem, said: “We had reports of dead fish in the lakes and we investigated at the end of last week.
“Dissolved oxygen levels in the water had crashed to about eight per cent when normally they are 70 to 80 per cent but had already started rising by themselves.
“This was due to atmospheric pressure and was a natural cause.
“Thousands of fish died, mostly roach and bream with a few carp.
“There were still live fish in the water.
“It is unlikely that the lakes can be restocked until later in the year as these conditions can happen repeatedly in the summer months when the weather is hot.”
Kinewell Lake is a former gravel pit alongside the river Nene in Ringstead, which is owned by the village and managed by Kinewell Lake Trust.
A spokesman for East Northamptonshire Council said: “Kinewell Lake at Ringstead is owned by Ringstead Parish Council and so they have been liaising with the Environment Agency about the death of fish in the lake.
“The parish council should make their own provision for disposing of the fish and will work with the Environment Agency to ensure the water returns to a suitable standard for fishing stock.”