The U.S. Army Corps of Engineers declined to endorse a single plan after studying the matter since 2009, disappointing sponsors of legislation that ordered the agency to move faster. Instead, the Corps provided a 232-page analysis with eight possible approaches.
Two would place dams in the Chicago waterway system to seal off Lake Michigan from the carp-infested Mississippi River watershed. Environmentalists and five states that unsuccessfully sued the Corps in federal court favour that approach, while Illinois, Indiana and local shipping interests oppose it.
Other proposals would use different mixtures of equipment and technology, including construction of additional electric fish barriers and a new type of navigational lock that would treat water to remove floating plants and fish as vessels move through the system.
Bighead and silver carp are a big concern for the Great Lakes because they could threaten a fishing industry valued at $7 billion a year. Also, silver carp are notorious for springing from the water when disturbed by motorboats and colliding with their occupants, posing a risk to outdoor recreation.
Dave Wethington of the Corps' Chicago district office, project manager for the study, said battling invasive species is "a shared responsibility" that will require support from Congress and state governments, which would have to settle on a strategy and provide the money.
"We're providing this information to the decision-makers," Wethington said in a phone conference. "We are standing by to move forward to the next step."
The Great Lakes and Mississippi watersheds share a boundary nearly 1,500 miles long. But the study focused on a network of rivers and canals in and near Chicago with five direct links between the two giant drainage basins, considered the likeliest route by which Asian carp could reach the lakes.
The Chicago waterways are connected to the Illinois River, where a large carp population has advanced to within 55 miles of Lake Michigan. The Corps says an electric barrier 37 miles from the lake is preventing any individuals from slipping through. Scientists have detected Asian carp DNA in dozens of water samples past the barrier, although whether they came from live fish remains in dispute.
The Corps said the measures in its report could shut down pathways for 13 potential animal and plant attackers, from the bloody red shrimp to reed sweetgrass and a deadly fish virus. But public and congressional interest is riveted on bighead and silver carp — voracious Asian fish imported in the early 1970s to gobble algae in Deep South fish ponds and sewage plants.
They escaped during floods and have migrated up the Mississippi and Ohio rivers and tributaries in more than two dozen states. Scientists say they can destabilize ecosystems by devouring plankton, a vital link in aquatic food chains.
U.S. Sen. Debbie Stabenow, a Michigan Democrat, and Rep. Dave Camp, a Michigan Republican, said the Corps should have picked one approach and developed it more thoroughly. They favour separating the two watersheds and sponsored a bill that would do that.
"The only real solution that will truly protect the Great Lakes is the complete separation of the Great Lakes and Mississippi River," said Rep. Candice Miller, a Michigan Republican.
Two options in the Corps' report would achieve that by placing barriers along the Lake Michigan waterfront or farther inland. Both would severely disrupt commercial shipping and pollute the lake by preventing Chicago sewer discharges from flowing downstream as they do now, the report said.
Two other alternatives would use barriers to cut off some of the aquatic pathways while deploying additional electric barriers, screened gates, locks and water treatment plants.
The options achieving the greatest degrees of physical separation tend to be most expensive and time-consuming, with costs reaching $15 billion to $18.4 billion and a 25-year timetable. That's because they would require extensive reworking of Chicago's flood-control and sewage treatment systems in addition to building the dams, Wethington said.
The report also offers two middle-of-the-road alternatives that would maintain the waterway system's current shipping operations. One could be carried out in 10 years and cost $7.8 billion, a relative bargain. It would create a "buffer zone" with a series of control technologies.
Aside from doing nothing new, the cheapest approach would step up use of existing measures such as netting carp and treating the water with chemicals, at a cost of $68 million a year.
American Waterways Operators, a group representing barges and tugboats in the Chicago area, said the report makes clear that physical separation "is neither economically feasible nor will it be effective at eliminating all identified pathways for the spread of invasive species, including Asian carp."
Link to report: http://1.usa.gov/1kmJeYq
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