CHICAGO (AP) — The Illinois Department of Natural Resources and the U.S. Fish and Wildlife Service are set to begin rooting out heat-seeking Asian carp that have made it past the Chicago area’s electric fish barrier system.

While DNA samples suggest that destructive silver or bighead Asian carp have breached the barriers, no physical fish — dead or alive — has ever been found on the other side of them, said Chris McCloud, spokesman for the natural resources department.

Weather permitting, biologists will begin sampling in rivers and canals on Wednesday.

“We have got to find where these fish are at so we can hopefully validate the (DNA) evidence,” McCloud said.

Crews will focus on areas where warm water from industrial operations enters the waterways. Fish tend to congregate near the warmer water in the winter as temperatures drop. Workers and fishermen will use commercial fishing nets and electrofishing to search over the next two to three weeks, officials said.

In December, wildlife officials discovered a single Asian carp in a canal leading to Lake Michigan, the nearest the species has come to the Great Lakes. Environmentalists fear that if the carp reach the lakes they could starve out native fish species and devastate a $7 billion-a-year fishing industry. Carp can grow to 4 feet in length and 100 pounds.

Michigan has asked the U.S. Supreme Court to order Chicago-area shipping locks closed, a request supported by Minnesota, Wisconsin, Ohio, Pennsylvania and New York. Illinois opposes the closure. An Obama administration proposal on controlling carp also rejects closing the locks.

Other plans to fight back against the carp include having commercial fishermen help to thin out the populations in the waterways downstream from Chicago, which will take some pressure off the electric barriers, McCloud said.