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An Underwater Fence to Stop Invasive Species

By Kari Lydersen
Washington Post Staff Writer
Monday, July 9, 2007

A century ago, engineers blasted the Chicago Sanitary and Ship Canal out of limestone to reverse the Chicago River, an unprecedented engineering feat that linked Lake Michigan with the Mississippi River.

The project served its purpose, sucking water from the lake to flush out the growing city's waste, but there was an unintended consequence: It created a pathway between two previously distinct ecosystems and a route for invasive species traveling in both directions. Until recent years, though, heavy pollution in the canal prevented fish from swimming through it.

Today, the canal is cleaner, and the infamous Asian carp and the round goby are both threatening to take advantage. But the government is stepping up its efforts to stop them.

The carp, prolific filter feeders that wipe out food supplies for other fish, have been slowly making their way up the Mississippi since escaping into the wild after they were imported in the 1960s and '70s to control algae in Southern fish farms.

The voracious carp, which can grow to 50 pounds, are within 50 miles of the lake, and the only thing stopping them from completing the journey is an underwater "electric fence," which the U.S. Army Corps of Engineers constructed under the canal. It was activated in 2002 -- the first such barrier ever installed in a navigable waterway.

The U.S. Fish and Wildlife Service monitors the advance of the Asian carp with an annual "carp corral," in which workers count the carp netted at checkpoints along a stretch of the Illinois River.

During the corral last month, at a spot in the river about 100 miles from Chicago, scores of bighead and silver carp rocketed into the air, stirred by vibrations from boats.

"We've had lots of broken noses and damaged boats," said Pam Thiel, a project director of the U.S. Fish and Wildlife Service.

The survey netted more than twice as many Asian carp at that location as last year: 241, compared with 110. "They haven't moved much upstream since 2002, but their numbers are increasing," Thiel said.

The underwater barrier has outlived its predicted five-year life span; the bundles of steel cables, which electrify a 54-foot-long stretch of canal with a one-volt-per-square-inch charge, are still working.

People feel just a tingle, or nothing at all, if they stick their hands in, Corps engineers say. But the effects could be more serious if someone were to fall into the canal. The Corps is working with the U.S. Navy to figure out, through modeling, how the electricity would affect a person who falls overboard.

"If someone were to fall in the water, what would happen?" asked Commander Paul Mehler III, commanding officer of the U.S. Coast Guard Marine Safety Unit Chicago. "We really don't know."

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.

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