An Underwater Fence to Stop Invasive Species

Electric barriers are regularly used on fish farms and in small streams, said Corps of Engineers project director Chuck Shea, but the Chicago project has yet to be tested by the Asian carp it was built to thwart. The Corps did test it with common carp, a long-established, less-harmful species. Tagged with transmitters, they were released nearby to see if they crossed the barrier. Only one has made it so far, probably riding the turbulence from a passing barge.

"Results show the barrier is working," Shea said. "Depending on how brave or gutsy a fish may be, some may go a little further than others before turning back."

The Corps is planning to replace the original barrier with a new, more powerful one capable of lasting at least 20 years, but that project is in limbo because of funding shortfalls and safety concerns.

Half of the new "fence," known as Barrier 2A, is completed, but it cannot be turned on because sparks have been seen jumping between barges that collided in the electrified area; such sparks could trigger an explosion or injure crew members. The Corps, contractors Smith-Root and the U.S. Coast Guard are trying to figure out how to solve that problem. In the meantime, the Coast Guard has barred barges from mooring or passing in the area of the old barrier.

The two halves of the new barrier would each consist of a 130-foot stretch of electrified steel rods running under the canal, with 220 feet in between each half.

To finish the job, however, the Corps needs an estimated $6.9 million beyond the original $9.1 million price tag. The funding is included in the Water Resources Development Act, which is in the hands of a congressional conference committee.

Joel Brammeier, associate director of the Alliance for the Great Lakes, said congressional action to finish the barrier is desperately needed, but it is already too little, too late.

"This should have been built and turned on years ago, but it's still a temporary solution to a permanent problem," he said. "We connected two ecosystems that had evolved separately, and, by developing Chicago around this waterway, we've created a thriving economy but also a problem of fish being where they shouldn't be. We need to take steps to bring these things into balance. What that solution looks like is still up in the air."

The barrier will probably block the Asian carp, but it's a different story for fish heading downstream out of the Great Lakes toward the Mississippi, such as the round goby. Round gobies, which entered the Great Lakes in ballast water pumped out by visiting ships, eat endangered native mussels and other species' eggs.

"Most of our native fish spawn once a year, and round gobies spawn every 20 days, so they out-compete" the local species, Thiel said.

Fish entering the Mississippi and its tributaries from the Great Lakes represent a special threat because of a deadly fish virus known as viral hemorrhagic septicemia, which has been killing fish in every Great Lake except Lake Superior.

Some made their way past the site of the original barrier before it was built. Shea said the barrier is probably slowing down other fish that try to follow, but Brammeier said eggs and young from round gobies and other species can float downstream through the barrier.

"The barrier won't prevent all life stages of all species from moving between the Mississippi and Great Lakes," he said.

It may also take a higher voltage to stop smaller fish such as the round goby, since their smaller surface area makes them less vulnerable to electric shock. The new barrier will be capable of delivering three to four volts per square inch, more than triple the capability of the first barrier.