The Obama administration opposes closing shipping locks near Chicago to prevent Asian carp from invading the Great Lakes.
In a memo filed Tuesday, Solicitor General Elena Kagan asked the U.S. Supreme Court to reject a request by Michigan and several other states to order the locks closed. Illinois filed a document supporting the administration's position.
Kagan says closing the locks would endanger public safety and disrupt cargo.
She says federal agencies are working to keep Asian carp out of the lakes.
The voracious fish have been migrating up the Mississippi and Illinois rivers toward the Great Lakes for decades. They have infested waterways near Chicago leading to Lake Michigan.
Scientists say if they reach the lakes, they could disrupt the food chain and endanger the $7 billion fishery.