MONTREAL — Like a slippery alien from a science-fiction movie, the Asian carp, a fish species that can grow four feet long (1.2 m), weigh up to 110 pounds (50 kg), and leap eight feet (2.4 m) out of the water, could invade the Great Lakes where it would eat its way through the ecosystem, experts warned Thursday.

Nonnative to North America, the carp are migrating at the rate of 50 miles (80 km) a year up the Illinois River toward the Chicago Ship and Sanitary Canal at Romeoville, Ill., which connects the Mississippi River system to the Great Lakes.

Fears are they could reach Lake Michigan this year, according to the International Joint Commission (IJC), a body established by Canada and the United States to help protect the Great Lakes waterways the two countries share.

"The IJC believes that the Asian carp have the potential to seriously damage or destroy the Great Lakes ecosystem and that the threat is imminent," said Dennis Shornack, chairman of the commission's U.S. section. "These fish consume vast amounts of food. They are highly prolific and can quickly grow to a size at which they have no natural predators," he said.

Imported from China by southern U.S. fish farmers in the early 1970s, the big carp have already cut a swath through local species on its journey northward. "Commercial fisheries in some parts of the Lower Mississippi have been completely destroyed by the invasion of Asian carp," Shornack added.

Experts said the fish can consume up to 40 percent of their body weight daily in vegetation, zooplankton, or native mussels and fish. Each female carries up to 1 million eggs, allowing the carp to quickly displace natural species of fish in local habitats.

ONE CARP FOUND IN FOUNTAIN

Herb Gray, Canada's former deputy prime minister and chairman of the Canadian section of the commission, warned that a public education program is needed to prevent people from introducing the carp into the Great Lakes. Two live specimens have already be captured in the area. "One bighead carp was collected in a net in Lake Erie by scientists from the University of Guelph, and another was found in a fountain in downtown Toronto," Gray said.

Three kinds of Asian carp — silver, bighead, and black — escaped from U.S. fish farms into the Mississippi River system during floods in the early 1990s. Used in aquaculture to control algae and snail populations, the carp population quickly bloomed in nature and began moving northward to coolers waters that are their natural habitat.

The carp are now within 25 miles (40 km) of Lake Michigan, and the best defense against them may be a $2.2 million electric barrier built under the Chicago canal by the U.S. Army Corps of Engineers. Originally designed to keep another invasive species, the round goby, out of the Mississippi, the barrier was turned on in April 2002 and uses a low-charge electrical current to repel fish.

The problem is that the barrier is an experimental prototype and is scheduled to be removed in October 2003. The design and funding also do not provide for a backup generator to keep it operating in the event of a power failure.

In a letter sent last week to U.S. Secretary of State Colin Powell and Canadian Foreign Affairs Minister John Manley, the commission called for immediate action to block the Asian carp, including building a second, permanent barrier in the canal.