Image: Tow boat in Chicago canal
Scott Olson  /  Getty Images
Tow boats like this one and other ships rely on the Chicago Shipping and Sanitary Canal and its locks.
updated 1/19/2010 11:39:57 AM ET 2010-01-19T16:39:57

The U.S. Supreme Court on Tuesday refused to order immediate closure of shipping locks near Chicago to prevent Asian carp from infesting the Great Lakes.

The court rejected a request by Michigan for a preliminary injunction to close the locks temporarily while a long-term solution is sought to the threatened invasion by the ravenous fish. The one-sentence ruling didn't explain the court's reasoning.

Asian carp, primarily big head and silver varieties, have been migrating up the Mississippi and Illinois rivers toward the Great Lakes for decades. They have swarmed waterways near Chicago leading to Lake Michigan.

Scientists fear that if they reach the lakes, they could disrupt the food chain and endanger the $7 billion fishery.

The biggest Asian carp can reach 4 feet in length and weigh 100 pounds while consuming up to 40 percent of their body weight daily in plankton, the foundation of the Great Lakes food web.

Native species threatened
Many scientists say they could starve out popular species such as trout and salmon.

They also are spooked by passing motors and often hurtle from the water, colliding with boaters forcefully enough to break bones.

Officials poisoned a section of the canal in December after discovering genetic material that suggested at least some carp might have eluded an electric barrier on the Chicago Sanitary and Ship Canal and could be within six miles of Lake Michigan. If so, the only other obstacles between them and the lake are shipping locks and gates.

Last week, the U.S. Army Corps of Engineers said additional carp DNA — but no live fish — had been found in three different spots along the Chicago River within a mile of where it flows into Lake Michigan.

5 states, Canadian province want locks shut
Michigan, joined by Minnesota, New York, Ohio and Wisconsin and the Canadian province of Ontario, asked the high court to order the locks closed as a stopgap measure while considering a permanent separation between Lake Michigan and the Mississippi River basin.

Image: Asian Carp
M. Spencer Green  /  AP
These Asian big head carp were on display at a conference on Jan. 12 in Chicago, Ill., called to deal with the nonnative species.
"While this action means that the court will not order an immediate closure of the locks ... it does not mean that no action will be taken in the case," said Josh Mogerman, spokesman for the National Resources Defense Council. "There is still a significant possibility that the court will issue a decision regarding Michigan's broader requests for action on this issue."

The state of Illinois, backed by the Obama administration, fought the proposal. They said the DNA samples weren't sufficient evidence that the carp were on the verge of slipping into Lake Michigan, and said closing the locks would damage shipping and passenger traffic on the busy waterway.

A message seeking comment was left Tuesday with Illinois Attorney General Lisa Madigan's office.

Copyright 2010 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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