TRAVERSE CITY, Mich. (AP) - Asian carp are unlikely to reach the Great Lakes by stowing away on commercial vessels in Chicago-area rivers and canals, the U.S. Coast Guard said Thursday.

Even if the invasive fish somehow got into the ballast tanks of vessels early in their life cycle, they almost certainly would be killed in pumping mechanisms through which they’d have to pass to return to open water, researchers found in a recent study. Ballast tanks are the compartment of a ship that holds water, which helps it maintain buoyancy.

Scientists with the Coast Guard Research and Development Center and the U.S. Environmental Protection Agency conducted experiments in a section of the Illinois River called the La Grange Reach, where Asian carp are well established.

Bighead and silver carp imported from Asia decades ago have infested the Mississippi River and many of its tributaries. An electric barrier in a shipping canal near Chicago is meant to keep them from migrating into Lake Michigan, where scientists say they eventually could spread to the other Great Lakes and out-compete native fish for food.

But scientists in recent years have detected DNA from Asian carp in waterways beyond the barrier, sparking debate over its effectiveness. Some advocates want billion-dollar barriers constructed to seal off Lake Michigan from the Mississippi watershed, which opponents say would disrupt shipping traffic and cause flooding around Chicago.

State and federal experts are studying whether the DNA could have come from sources other than Asian carp. They’re also considering ways the fish might be evading the barrier. One theory is that carp eggs, larvae or recently hatched fish might slip through cracks in hulls of barges and tugboats and enter the ballast tanks. If they survive as the vessels move through the electric field, perhaps they could escape back into the water on the other side.

But results of the study show only a “minimal risk” of that happening, the Coast Guard said in a news release.

The Coast Guard researchers cut 3-inch holes on the exterior of a barge’s ballast tanks and installed valves to determine whether larvae could get inside through hull ruptures. They also placed carp larvae inside a tank to monitor how long they’d survive and pumped water out of the barge tanks to see if larvae could live through the process.

A few tiny fish did get into the tanks, and the water inside had enough oxygen for them to survive temporarily, said Scott Anderson, chief of the prevention division for the Coast Guard’s 9th District in Cleveland. But almost none made it past the spinning rotor inside the pump that empties the tanks, he said.

“If they actually were able to get into (the ballast tanks) through cracks or holes, which was found unlikely, the mortality rate was over 99 percent when they were pumped back out,” Anderson said.

The study was funded through the Great Lakes Restoration Initiative, an Obama administration program aimed at making progress on some of the region’s biggest environmental problems. A detailed report is scheduled for release later in March.