CHICAGO (AP) — Officials say genetic material from Asian carp has been detected near Lake Michigan, but a follow-up search turned up none of the invasive fish.

The U.S. Fish and Wildlife Service posted results last week from sampling conducted in the Chicago Area Waterway System in early April.

Most of the 401 water samples were negative, but six registered DNA hits for silver or bighead carp in Lake Calumet, a few miles from Lake Michigan.

Scientist say if the fish become established in the Great Lakes, they could out-compete native species.

Asian carp DNA has been found repeatedly in Lake Calumet and other spots beyond electric barriers intended to block them.

An official with the federal agency told the Milwaukee Journal-Sentinel crews searched for live Asian carp last week but found none.