WASHINGTON (CBS) — The U.S. Supreme Court has decided not to order the closure of locks on the Sanitary and Ship Canal to keep the Asian carp out of the Great Lakes.

The high court on Monday refused to hear an appeal of a lawsuit filed by the State of Michigan and other Great Lakes states, which all want the locks on the canal to be shut down at once. They are also seeking a quicker timetable for other steps to halt the carp’s northward march from the Mississippi River toward Lake Michigan.

The Supreme Court already has rejected the request from Michigan, Minnesota, Ohio, Pennsylvania and Wisconsin twice.

The states have a pending lawsuit that calls for permanently severing the canal, which links the Mississippi and Great Lakes drainage basins. They wanted a court order to close the locks while their suit works through the courts.

Attorneys general from the four states – as well as the State of New York – have also issued a letter asking colleagues along the Mississippi River to encourage the U.S. Army Corps of Engineers to close the canal voluntarily.

In addition, two environmentalist groups – the Great Lakes Commission and the Great Lakes and St. Lawrence Cities Initiative – said the canal must be closed to keep the voracious fish from entering the Great Lakes and damaging the ecosystem.

Currently, electronic barriers are in place on the Sanitary and Ship Canal to keep the Asian carp out of the Great Lakes.

So far, although Asian carp DNA has been found in Lake Michigan, only one actual Asian carp has been found on the lake side of the electronic barriers to date, in Lake Calumet.

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