The Prospect Park Alliance says the humid and hot weather is causing fish to die in Prospect Park Lake.
News 12 meteorologist Mike Favetta says the borough is currently in a rainfall deficit of 6 inches.
"Warmer summer nights have contributed to a lot of this excess heat, and that is absorbed by the water - thus depleting the oxygen," says Favetta. "We all know that fish need oxygen in order to survive."
The lake is popular for fishing, although it is strictly a catch and release area.
The alliance says it has asked the state Department of Environmental Conservation to investigate and confirm the cause.