WASHINGTON (Reuters) - The U.S. Supreme Court on Tuesday rejected a request by the state of Michigan for an injunction to force the closing of two Chicago-area waterway locks to keep the Asian carp from invading the Great Lakes.

The voracious Bighead and Silver carp are considered a dire threat to the lakes’ $7 billion fisheries.

The state last month took the unusual step of asking the high court for an order that would close the two locks and would require authorities to take all other action necessary to keep the carp from entering the lakes.

Michigan asked that the U.S. Army Corps of Engineers, the state of Illinois and Chicago’s sewer authority take more steps to block the carp during flooding and ultimately to separate the Great Lakes from the Mississippi River watershed.

Closing a lock and dam and the other measures could help keep the carp from entering the lakes, but it also court hurt shippers, who transport 15 million tonnes of commodities through the connecting waterways each year.

Nearby Midwestern states such as Minnesota and Ohio supported Michigan’s request while Illinois and the federal government opposed it.

U.S. Solicitor General Elena Kagan told the court that Michigan failed to show likely irreparable harm, that the state cannot prevail on the merits of its theory and Michigan cannot justify the mandatory relief it demands.

If the Army Corps makes a final decision to reject the steps Michigan wants, then the state can ask a federal judge to decide if the agency acted lawfully, Kagan said.

While the court rejected the preliminary injunction, it took no action on Michigan’s separate request to reopen cases dating back to the 1920s that control how much water Chicago can withdraw from Lake Michigan.

A huge engineering project a century ago reversed the direction of the Chicago River and diverts lake water into a canal that connects Lake Michigan to the Mississippi River watershed. The goal was to stop sewage releases into the lake.

Kagan said Michigan was trying to use old cases about water flows and allotments to litigate an entirely different environmental protection issue involving the carp.