Great Lakes Article:

(AP) At one time the Chicago River was so polluted that no fish could live there, and now scientists are considering a longshot idea to make it unlivable again to prevent exotic species from using the river to migrate between the Mississippi River and Great Lakes.

Killing the river would buck the Clean Water Act and set an ugly example of environmental policy. But biologists foresee ecological and economic disaster from invasions of giant carp, zebra mussels and other undesirables.

"We've done marvelous things with the Clean Water Act, and nobody wants to undo that," said Jerry Rasmussen, a river biologist for the Fish and Wildlife Service.

The Chicago River flows backward, away from Lake Michigan, because 19th century Chicagoans engineered it to carry pollution away from their beaches and into a canal. The canal flows to the Illinois River, a tributary of the Mississippi, creating a link unintended by nature.

Until aerators were used in the 1970s to pump oxygen into the water, Chicago's waste polluted the river and canal. The Metropolitan Water Reclamation District has since brought the manmade waterway into federal compliance.

But now that the waterway can support native fish, nonnative invaders can live there too.

Zebra mussels, drifting from Lake Michigan to the Mississippi 300 miles away, have cost an estimated $5 billion in clogged water intakes and damage to fisheries, according to the Environmental Protection Agency.

Asian bighead carp are swimming in the other direction. The 100-pound, plankton-straining species were imported to clean Mississippi Valley fish farm ponds. They escaped during floods and are within 25 miles of Lake Michigan.

Rasmussen and others fear bigheads could destroy the lakes' food chain.

As a coordinator at the agency's Rock Island office, Rasmussen suggested river-killing among several options in an analysis for cooperating agencies.

States routinely use smaller kills to eliminate nonnative or "trash" fish. In September, Maryland poisoned a 4-acre pond to kill more than 1,000 rapacious Asian snakehead fish.

The Illinois Natural History Survey is testing options at its lab in Havana on the Illinois River. Bighead carp dominate the river there, after reaching the stretch in the mid-1990s.

"We'll catch easily 100 before we even get the net set," station director Mark Pegg said.

In tests, electrodes were only 98 percent effective. The success rate for a combination of underwater noise and a wall of bubbles was about two-thirds.

Testing a combination of bubbles, noise and electrodes is next. Then, heated water and a nitrogen plume that would suffocate the channel as waste once did. Some suggestions are as simple as bringing in predators.

Mayor Richard Daley is lobbying Congress and agencies for more barrier funding but is uncertain about the river-killing proposal, city Environment Commissioner Marcia Jimenez said. She said the city wouldn't endorse shutting off aerators "without a great deal of research."

Even building a dam wouldn't guarantee protection against the Asian carp.

"Someone may like to eat them and decide it's a good idea to release them," said Sarah Whitney, program manager with the Great Lakes Commission in Ann Arbor, Mich.

Still, she said, there's no sense giving up.

"Otherwise I'd just go home and cry," she said.