The U.S. Army Corps of Engineers have constructed an electric barrier in the Chicago Sanitary and Ship Canal, a waterway linking the Mississippi River with the Great Lakes watershed. The idea is to prevent Asian carps from entering the Great Lakes where it could wreck havoc with the ecosystem.

Seven species of carps native to Asia have been introduced to the United States, and four of them are considered a threat to the Great Lakes: bighead carp, silver carp, black carp and grass carp.

The new electric barrier is located slightly upstream from two similar barriers in the canal, and consists of underwater electrodes that creates a forced field by emitting rapid pulses. The force field is meant to repel fish and is capable of shocking those that refuse to turn around.

“We now have great flexibility and redundancy”, says Col. Vincent Quarles, commander of the Army Corps’ Chicago district. “We want to deter the Asian carp threat. The barrier is a very good tool.”

Since the early 1970s, Bighead carp and Silver carp have migrated northward on the Mississippi and its tributaries. Environmental groups have called for physically severing the man-made Chicago Sanitary and Ship Canal, which was completed in the year 1900 to connect the Great Lakes with the Mississippi drainage basins.

Michigan and four other Great Lakes states also wish to sever the canal, and there is currently a federal lawsuit pending against the Army Corps. The Army Corps have pledged to consider that option in a comprehensive study, but that study is not scheduled for completion until 2015.

The first electrical underwater fence in the Chicago Sanitary and Ship Canal was activated in 2002, while the second one was turned on seven years later. Federal and state officials say that the barriers have performed well, but skeptics keep questioning the effectiveness of the barriers. Scientists with the University of Notre Dame and The Nature Conservancy have reported findings of DNA from both Bighead carp and Silver carp in numerous locations above the barriers. However, no Asian carps have been found, save for one single specimen.

“There are still serious gaps in our knowledge about how well it’s working,” says Thom Cmar, an attorney with the Natural Resources Defense Council. “No one ever imagined these electric barriers would be a permanent solution. They’ve always been just a stopgap idea.”

In a newly released report, the Army Corps acknowledges that the 2 volts per inch used in the barriers may not be enough to deter small fish that are just a few inches in length. Increasing the voltage might however endanger the ships moving flammable items across the canal.