CHICAGO Authorities scooped up poisoned fish floating to the surface of a Chicago-area waterway on Thursday in an operation designed to keep invasive Asian carp out of the Great Lakes and prevent an ecological disaster.
Illinois officials said a single Bighead carp, one of two prolific species of Asian carp viewed as a threat, had turned up in the huge fish kill that began overnight along 6 miles of the Chicago Sanitary and Ship Canal southwest of the city.
Poison was dumped into the waterway so maintenance could be performed on an electrical barrier that is designed to keep the carp out of the Great Lakes.
The Asian carp was found some 40 miles from Lake Michigan, which was the closest to the Great Lakes the species has been found, authorities said.
Some 200,000 pounds (90 tons) of dead fish are expected to be collected, weighed, inventoried, and dumped in a landfill over the next few days. Most of the dead fish scooped up so far have been native carp and shad.
Silver carp and the Asian Bighead, which can grow to 5 feet and weigh more than 100 pounds (45 kg), have come to dominate sections of the Mississippi River and its tributaries.
Authorities fear that if the carp swim up to the Great Lakes, the largest fresh-water resource in the world, they could create an "ecological disaster" by consuming the bottom of the food chain and ruining the lakes' $7 billion fishery.
Since 1990s floods allowed the carp to escape into rivers from research facilities and commercial fish ponds in the South, where they were introduced to clean away weeds and other detritus, the carp have multiplied and become a "nuisance species," according to the U.S. Fish and Wildlife Service.
Along some stretches of the Illinois River, the carp make up 95 percent of the biomass and they are considered poor for eating or as a game fish. Silver carp, which leap into the air when disturbed by passing motorboats, have injured boaters.
Two electrical barriers in the canal were erected in 2002 and 2006 to shock any fish, particularly carp, that try to swim up the canal to Lake Michigan. The newer barrier is being switched off to perform maintenance on it.
To give themselves a window to complete the task and keep any carp at bay below the barrier, authorities dumped into the canal more than 2,000 pounds (900 kg) of the natural poison rotenone that prevents fish gills from absorbing oxygen.
The toxin, which is used as a broad-spectrum insecticide and pesticide, kills fish and freshwater snails but does not harm other animals. It dissipates within two days, though authorities planned to introduce a neutralizing agent to speed up the process.
Notre Dame University scientists recently detected carp DNA on the lake side of the barriers, which could indicate the carp have already passed them and the effort is either too little or too late.
Fishermen have been asked to look out for the invasive carp on the lake side of the barriers.
The DNA discovery led some environmentalists to call for river locks to be shut and ask for permanent separation of the Great Lakes from the Mississippi River watershed.
Michigan Governor Jennifer Granholm has indicated her state might demand locks be closed permanently.
But the shipping industry argued that would be a costly mistake.
The American Waterways Operators, which represents barge operators and other water shippers, said 15 million tons a year of commodities including oil, cement, iron, coal and road salt would be disrupted or halted.
(Editing by Eric Beech)