TRAVERSE CITY, Mich. (AP) — Asian carp may have breached an electronic barrier designed to prevent the giant invaders from upsetting the ecosystem in the Great Lakes and jeopardizing a $7 billion sport fishery, officials said Friday.

Scientists recently collected 32 DNA samples of Asian carp between the barrier and Lake Michigan in waterways south of Chicago, although the fish have yet to be spotted in the area, said Maj. Gen. John Peabody of the U.S. Army Corps of Engineers.

If the feared bighead and silver carp have got through the $9 million barrier, the only remaining obstacle between the carp and Lake Michigan is a navigational lock on the Calumet River. Some DNA was found as close as 1 mile south of the lock and 8 miles south of the lake.

Still, federal officials insisted a Great Lakes invasion was not inevitable.

"We're going to keep throwing everything we possibly can at them to keep them out," said Cameron Davis, senior Great Lakes adviser to Lisa Jackson, head of the Environmental Protection Agency.

Asian carp escaped from Southern fish farms into the Mississippi River during 1990s flooding and have been migrating northward since.

The monstrous creatures can exceed 4 feet long and 100 pounds. They consume up to 40 percent of their body weight daily in plankton, starving out smaller and less aggressive competitors.

Aside from decimating species prized by anglers and commercial fishers, Asian carp are known to leap from the water at the sound of passing motors and sometimes collide with boaters.

It is not known how the carp would fare in the chilly Great Lakes, which are different ecosystems than rivers, Davis said.

A worst-case scenario envisions them spreading "like a cancer cell," he said, eventually dominating a fishery already damaged by zebra mussels, sea lamprey and other exotic pests.

In 2002, the Army Corps placed an electronic device on the Chicago Sanitary and Ship Canal, a man-made waterway south of the city that forms part of a linkage between the Mississippi and Lake Michigan.

A second, more powerful device went online this year. Both emit electrical pulses designed to repel the carp or give them a non-lethal jolt.

David Lodge, a University of Notre Dame invasive species expert, confirmed the presence of DNA of bighead and silver carp in the Cal-Sag Channel, between the canal to the Calumet River and in the river itself, which flows into Lake Michigan.

Further testing will be done in the area, said Col. Vincent Quarles, the Army Corps' Chicago district commander.

The newer electronic device is scheduled to be deactivated for maintenance in early December. Officials plan then to treat a 6-mile section of the canal with a fish toxin called rotenone to prevent Asian carp from advancing.

Environmental groups called for tougher action, including closure of all Illinois gateways and locks leading to Lake Michigan. That would draw opposition from barge companies that haul cargo on the canal.

"If we don't close the locks, we are waving the white flag and allowing one of the greatest ecological tragedies to occur," said Jennifer Nalbone of Great Lakes United.

Even if the carp reach the lake, it might be possible to limit their spread with methods such as sterilization.

"We should not assume that all is lost," Lodge said.