MADISON (WMSN) -- Wisconsin is getting ready to join the legal fight to keep Asian carp out of the Great Lakes.



The big head and silver carp are invasive species that could devastate the health of Wisconsin's waterways.



They've been documented swimming in Illinois rivers -- 40 miles from Lake Michigan.



Attorneys general from Minnesota, Michigan, and Ohio have already filed papers with the United States Supreme Court, suing the state of Illinois, and requesting all be done to stop the carps' spread.



Wisconsin is getting ready to follow suit.



"Asian carp are voracious feeders," said Emily Green, Great Lakes director of the Sierra Club. "They grow to be 80 to 100 pounds and they are filter feeders. They eat plankton -- the base of the food chain."



The carp were brought to the southern U.S. from Asia in the 1970's. The fish eventually swam up the Mississippi and Illinois rivers. Only a man-made waterway -- the Chicago Sanitary and Ship Canal is keeping them at bay.



The threats are many -- with no known predators in North America, the fish could multiply, disrupting the food chain, and killing off prized game fish. The carp are also easily startled, and are known to propel several feet out of the water, injuring boaters.



"People who frequent the Illinois river a lot have carp cages that protect the boat's driver because they've had broken noses, broken ribs, broken arms from these 80 to 100 pound carp leaping out of the water and landing on them or in their boat," said Green.



And with 820 miles of Great Lakes shoreline, the carp could easily spread to Wisconsin's rivers and inland lakes.



"Water skiing, recreational boating, fishing -- if carp become established -- all that as we know it would end."



In December, Great Lakes states started rallying, urging officials to find the fish and kill them, by closing the Chicago Sanitary and Ship Canal.



"We are asking the Army Corps Of Engineers to do an emergency closure -- not necessarily permanent -- to find out where the fish are," said Green.



On December 4th, dozens of boats from the Army Corps and Illinois Department of Natural Resources combed the canal, dumping 2,200 gallons of the toxin rotenone, to kill any fish, and estimate the number of carp. Officials were worried the carp had breached an electronic barrier, but found only one carp.



Hundreds of millions of dollars in commercial barge traffic pass through the Chicago Sanitary and Ship Canal annually. Shutting it down could hurt some companies' bottom lines.



Wisconsin Attorney General J.B. Van Hollen supports the lawsuit against Illinois. "I am currently preparing Wisconsin's response to the United States Supreme Court," he said. "I remain deeply concerned about this matter and intend to present the best case to protect Lake Michigan."



Van Hollen says he will file papers with the U.S. Supreme Court by Thursday. Justices could take up the case by January 8th.



Green says there's too much at stake.



"If carp get into the Great Lakes there's not much we can do at that point. Right now, we have a chance to stop them."



The injunction would likely open decades-old court cases. Great Lakes states have been suing Illinois for a long time over the canal, and Chicago's water management.



It opened in the year 1900, long before the carp were introduced.



Online reporting by Jeff Angileri

Great Lakes states sue Illinois over Asian carp spread