A 3-foot-long Asian carp discovered in a Chicago waterway near Lake Michigan appears to have spent most of its life there and may have been planted by humans who did not know the environmental risk it posed, researchers said Thursday. Tests suggested it was not a recent arrival to the waterway and probably did not get there by evading an electric barrier meant to prevent the species from infesting the Great Lakes, said Jim Garvey, a biologist at Southern Illinois University Carbondale. The 20-pound bighead was netted June 22 in Lake Calumet. It was the first actual Asian carp seen above the barrier, and intensified calls by environmentalists and neighboring states to close shipping locks on the waterways.