CHICAGO (AP) -- A federal judge Monday threw out a lawsuit filed by five states that want barriers placed in Chicago-area waterways to prevent Asian carp from invading the Great Lakes, but said he would consider new arguments if the case were filed again.

Michigan, Wisconsin, Minnesota, Ohio and Pennsylvania claimed the U.S. Army Corps of Engineers and Chicago’s Metropolitan Water Reclamation District are causing a public nuisance by failing to physically separate a network of rivers and canals from Lake Michigan. Scientists have detected DNA from bighead and silver carp in the waterways. They say if the voracious carp become established in the Great Lakes, they could out-compete native species and severely damage the region’s $7 billion fishing industry.

U.S. District Judge John Tharp said he couldn’t order the agencies to do what the states want because federal law requires the corps to keep shipping channels open between Lake Michigan and one of the Chicago waterways -- the Des Plaines River -- and prohibits constructing dams in any navigable waterway without Congress’ consent.

In a written ruling, Tharp said he was "mindful of, and alarmed by, the potentially devastating ecological, environmental, and economic consequences that may result from the establishment of an Asian carp population in the Great Lakes." But he said the proper way for the states to win approval of separating the waterways is through Congress.

Tharp left the door open for further court action, however, saying the states might be able to find other grounds for a nuisance claim that wouldn’t have the effect of asking the corps and city agency to violate federal law. "There may be room in which the (states) can still maneuver," he wrote.

Joy Yearout, spokeswoman for Michigan Attorney General Bill Schuette, said his office had not decided on its next step.

"We’re certainly disappointed," Yearout said. "We’re reviewing the ruling and we will consult with the other states on how to move forward."