Three-hundred dead fish found at Priory Country Park in Bedford
About 300 dead fish have been found in a country park lake.
The Environment Agency said there was "no obvious cause" of the deaths of the bream at Priory Country Park, Bedford.
Bedford Borough Council said because of the "high level of mortality seen", the lake would not open for fishing as planned on 16 June.
It said tests showed "high levels of oxygen in the water, low levels of ammonia, algae and other potentially problematic microscopic plants".
Paul Wilkanowski, fisheries and biodiversity officer at the Environment Agency, said it had been investigating the lake since early May, when "cold temperatures" could have been a potential factor.
"Increasing water temperatures coinciding with the fish spawning period can often cause stress-related issues," he said.
Fishing in the lake has been put back to 1 July.
Liberal Democrat councillor Charles Royden, portfolio holder for environment at the council, said: "With estimates that 300 bream have died, it is only right that we delay the start of the season to limit the impact on our fish population.
"We will be monitoring the situation closely."
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