It's probably no coincidence that many of the positive samples have come from Chicago's Lake Calumet and western Lake Erie, where three bigheads were snagged in 1995 and 2000, the paper says.

WSJ: Report: Asian carp may have reached Great Lakes

Some of the Chicago DNA was found in Lake Calumet, where a live bighead carp was caught in 2010.

WSJ: Report: Asian carp may have reached Great Lakes