It is impossible to kill all of the exotic species sloshing between the Great Lakes and the Mississippi River basin, so some scientists suggest killing the river that links the two watersheds.
It is a radical long shot of an idea that goes against the federal Clean Water Act. Even the fact that some wildlife advocates would even think of returning the Chicago River to its former, sludgy self underscores the ecological and economic disaster wrought when Asian carp, zebra mussels and other undesirables emigrate.
"Take the oxygen out of the water," suggested Jerry Rasmussen, a river biologist for the U.S. Fish and Wildlife Service. "We've done marvelous things with the Clean Water Act, and nobody wants to undo that."
Shutting down the river's aeration system would effectively halt migration until scientists come up with a better answer, Rasmussen said.
Zebra mussels, now 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 U.S. Environmental Protection Agency. Now officials fear a repeat in the other direction, as giant carp work their way from the Mississippi toward the lake.
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.
Before aerators, in the 1970s, Chicago's waste choked the river and canal so that no fish could swim through and live. The Metropolitan Water Reclamation District has since brought the manmade waterway into federal compliance.
The new urgency comes with the Asian bighead carp, a potentially 100-pound home wrecker. Imported to clean Mississippi Valley fish farm ponds, the plankton-straining fish escaped in floods and are within 25 miles of Lake Michigan. Rasmussen and others fear bigheads could destroy the lakes' food chain.
As large river operations coordinator at the wildlife agency's Rock Island field office, Rasmussen made the river-killing suggestion as one of several options in an analysis he wrote for cooperating agencies.
Other state and federal biologists agree it could be effective but politically difficult.
States routinely use fish kills to remove nonnative or "trash" fish. In September, Maryland sprayed poison on a 4-acre pond to kill it and the more than 1,000 rapacious Asian snakehead fish in it.
City Environment Commissioner Marcia Jimenez said she worries about damage to other plants and animals and would not endorse shutting off aerators "without a great deal of research."