The U.S. Supreme Court on Tuesday said it would not help stop the spread of invasive Asian carp by ordering the closure of locks between Chicago-area waterways and Lake Michigan. A suit from Michigan and four other states, plus Ontario, had requested closing the locks to block Asian carp from entering Lake Michigan and damaging its ecosystem, as they have done elsewhere in the country.

According to the U.S. Environmental Protection Agency, Asian bighead (Hypophthalmichthys nobilis) and silver (H. molitrix) carp were imported into the U.S. in the 1970s as a method to remove algae from catfish farms. But flooding in the 1990s overflowed farming ponds and sent the large, voracious fish into the Mississippi River, where they have managed to outcompete, outbreed and out-eat local species.

"We cannot allow carp into the Great Lakes. It will destroy our Great Lakes fisheries, the economy," Michigan Gov. Jennifer Granholm said in a prepared statement. The commercial fishing industry in the Great Lakes is worth more than $7 billion a year. The locks, meanwhile, are vital to shipping throughout the Great Lakes region.

So far, other attempts to block the northward invasion of Asian carp—including electric fish barriers and poisons—have not proved effective.

The Supreme Court didn't reveal any of the reasoning behind its ruling, which simply read: "The motion for preliminary injunction is denied."

Even if the locks had been closed, there's no guarantee they would stop the carp. Maj. Gen. John Peabody of the U.S. Army Corps of Engineers, which maintains the locks, told the Associated Press, "The locks are leaky, and there are alternate pathways around them."

And as if to prove that point, the Corps announced Tuesday that DNA from Asian carp has been found in Lake Michigan for the first time, although no actual carp have been observed. The DNA was found in water samples (pdf) taken from Calumet Harbor and the Calumet River.

"Clearly this is not good news," Peabody said in a statement, "But environmental DNA technology provides the advanced warning of the possible presence of Asian carp, so that all agencies supporting the Asian Carp Regional Coordinating Committee can focus their efforts and resources to optimal effect."

The Supreme Court's denial isn't the end of the story. Michigan's lawsuit continues, and Granholm plans to ask for a White House summit with President Obama and the other Great Lakes states governors. "We are asking for an immediate summit at the White House with the administration to shut down these locks, at least temporarily, until a permanent solution can be found," she said.

Image: Asian carp by Kate Gardner, via Flickr (Creative Commons license)