MILWAUKEE, April 22 (UPI) -- While authorities concentrate on keeping invasive Asian carp out of Lake Michigan, the fish are heading into Wisconsin's inland waters, officials said.

A commercial fisherman caught a 27-pound bighead carp Monday just north of the St. Croix River's confluence with the Mississippi and contacted the Minnesota Department of Natural Resources, the Milwaukee Journal Sentinel reported.


It was the sixth Asian carp found in Wisconsin-Minnesota border waters since 2003, officials said.

"This is not a crisis, but these fish are knocking on our door," said Luke Skinner, Minnesota DNR invasive species supervisor.

"We're concerned, but not surprised," said Mike Staggs, fisheries chief of the Wisconsin DNR. "The fish have found their way up here before. The hope is that it's just one adult, not a whole population."

Four species of Asian carp -- bighead, black, grass and silver -- are considered aquatic invasive species by Wisconsin and Minnesota.

Despite the latest catch, officials say they see no indication of a reproducing population of Asian carp in Wisconsin or Minnesota portions of the Mississippi or St. Croix rivers.

But that could change, expert said.

"Based on what we know of the fish, they have everything they need" to reproduce in the Mississippi and St. Croix rivers, Duane Chapman, research fish biologist for the U.S. Geological Survey, said.