The northern snakehead fish, native to China, Russia and Korea, has been spotted in Queens in recent years, and one was quietly observed in Harlem Meer several years ago.
The fish eats frogs and crayfish and has the ability to breathe air and live for days out of water in certain conditions. It is so disruptive that the state prohibits possession, sale and transport of the live fish and its eggs.
Signs have recently gone up around the Harlem Meer warning anyone who catches one not to throw it back.
The signs warn anglers to "secure the fish" and "keep it in a secure container until it is picked up by officials."
If park officials cannot be found at the boathouse, the sign urges anyone with a snakehead fish to call 311 and report the catch.
The sign is "just to let people know that this fish is in there, if you find it please do not return it to the water and it also helps people become aware that there are things in the water that should not be there," said Melissa Cohen, Department of Environmental Conservation fisheries manager.
The man-made lake is located in Central Park's northeast corner between 106th and 110th streets.