A huge amount of fish was found dead in the Mahabub Sagar tank located near Sanagreddy town on Wednesday morning.
Since the district had witnessed rains for the last five days, it received inflows from upstream.
Fishermen in the area suspect that some industries released harmful effluents into the tank resulting in the death of the fish.
The Fisheries Department officials collected samples of the dead fish and water, which would be sent for testing to find out the reason for the death.