Almost 2,500 fish have died in a reservoir in West Yorkshire.
The Environment Agency was contacted after members of the public contacted them after seeing distressed fish in the water at Doe Park Activity Centre in Denholme.
It is not yet known exactly what the cause is, but early examinations suggest an irritant has got into the water, reducing its quality.
One possible cause could be due to the change in weather as some of the fish were covered in a mucus-like substance. Yorkshire Water have been pumping oxygen into the water to improve conditions for the remaining fish.
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