Fish that have the potential to devastate the Great Lakes ecosystem may be just a few miles from Lake Michigan.

Two carp species from Asia — the silver and the bighead — are invasive fish with huge appetites. If they enter the Great Lakes, they could overwhelm the native fish.

To halt their migration, the U.S. Army Corps of Engineers built an underwater electric fence on a canal 20 miles south of Lake Michigan. Despite the barrier, tests now indicate that Asian carp have gotten close to the lake.

David Lodge, director of the Center for Aquatic Conservation at the University of Notre Dame, performed the tests. He says he used a new method to measure the fish's "environmental DNA" — and found that the carp were much closer to Lake Michigan than anyone previously thought.

"We have detected their DNA in places much closer to Lake Michigan than the traditional tools had told us," Lodge tells NPR's Robert Siegel. "You can think of this e-DNA as the equivalent for environmental protection of, say, using DNA in crime fighting to detect whether someone was at the crime scene. So, we don't actually have a body, but we have DNA."

The carp were originally brought to the United States to control nuisance algae — but they escaped and migrated to the Mississippi River basin, Lodge says.

He says he doesn't know the impact the carp can have on the Great Lakes "with certainty," but "there's lots of reasons to think they would be highly damaging."

The Mississippi and Illinois rivers serve as examples: 90 percent of what fishermen catch there are carp, and that has virtually destroyed commercial fisheries because carp has low commercial value, he says. What's more, silver carp have an "unusual habit" of jumping high out of the water — and have harmed people.

"They're like living missiles," he says. "And because they reach weights of up to 80 to 100 pounds, a fast-moving boat and a person sitting in it [colliding] with a fish is likely to come out much worse for the wear."

The plan has been to poison a 5- to 6-mile area near the canal to reduce the carp population below the electric barrier, Lodge says. He says it's important to go forward with that poisoning even though the new results show that the Asian carp are above the barrier.

"The game's not over; it's not time to give up," he says. "There are lots of examples of invasions that while [they] may initially look successful, may fail — or certainly be made to fail with effective management. We shouldn't give up at this point."

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