Commercial fishermen found the 3-foot-long, 20-pound carp in Lake Calumet on Chicago's South Side, about six miles downstream of Lake Michigan, according to the Asian Carp Regional Coordinating Committee.
While officials said they're concerned about the find, they need more information before deciding how significant it is.
"The threat to the Great Lakes depends on how many have access to the lakes, which depends on how many are in the Chicago waterway right now," said John Rogner, assistant director of the Illinois Department of Natural Resources.
Scientists and fishermen fear that if the carp become established in the Great Lakes, they could starve out popular sport fish and ruin the region's $7 billion fishing industry. Carp can grow to 100 pounds and 4 feet.
Joel Brammeier, president of the Alliance for the Great Lakes, said the carp's capture highlights the need for a long-term solution that goes beyond the electric current.
"Is it disturbing? Extraordinarily. Is it surprising? No," Brammeier said.
Rogner estimated that the male carp was about three to four years old. It was caught live but has since been killed and will be sent to the University of Illinois for additional analysis. The carp is the first to be found in a Chicago waterway above the Army Corps of Engineers' electric barrier system.
Officials said they'll use electrofishing and netting to remove any carp from the lake.
U.S. Sen. Dick Durbin said he's confident in the effort to contain the carp.
"Finding a solution that will protect our lakes, while preserving jobs and promoting economic activity in the region is essential," he said in a statement.