Chicago's waterways: The gateway for aquatic invasive species

The Chicago and Calumet Rivers are just thin trickles compared with the Mississippi River and the Great Lakes. But the health of the two vastly larger water systems relies, in part, on the pair of lowly rivers that flow through Chicago.

The Chicago and the Calumet are connected by the man-made Chicago Sanitary and Ship Canal to the Des Plaines River, which in turn flows to the Kankakee and Illinois Rivers, which eventually empty into the Mississippi. This complex network allows water to be exchanged between Lake Michigan and the Mississippi.

When the Sanitary and Ship Canal was completed in 1900, it "created a conduit, an artificial connection between the Great Lakes water system and the Mississippi River water system," according to Melanie Napoleon, director of Great Lakes conservation at the Shedd Aquarium.

Originally designed to carry ships and waste, the waterway now helps transport fish, plants and microorganisms between the lake and the Mississippi. This has given nuisance species like the zebra mussel, a shellfish from Russia that invaded the Great Lakes in the 1980s,  a chance to hop from one ecosystem to the other.

"The [Chicago] River plays a key role; it's a link between the two systems," says John Quail, the director of watershed planning for Friends of the Chicago River.

From one perspective, it's good news that the Chicago River can sustain life of any kind, given all the filth historically dumped into it.  Before the implementation of the Clean Water Act in the 1970s, and the cleanup of the river that followed, there was no problem with invasive species using the river as a freeway because they couldn't survive. 

"The dirty water didn't allow for a lot of live organisms to exchange through," says Steven Shults, aquatic nuisance species program manager with the Illinois Department of Natural Resources. "There's no biological barrier there anymore."

With cleaner water to breathe, non-native fish like the round goby -- first found in the Great Lakes in 1990 after presumably stowing away in some ship's ballast water -- could survive the trip out of Lake Michigan.  And non-native species become a problem when they out-compete the natives.

"They're fine in their native ecosystems," Napoleon says.  "They're part of the natural balance, the natural food web that is there.  They may have predators there, they may have pathogens or diseases."

With nothing to keep them in check, however, an invasive species will alter the biodiversity of an ecosystem, eliminating species that people and local economies depend upon.  That's exactly what silver and bighead carp, originally native to Asia, have been doing in the Mississippi River basin.

"Their numbers are so incredibly high," says Patrice Charlebois, an aquatic invasive specialist with the Illinois Natural History Survey. The carp "reduce the number of species that people angle for."

Asian carp can grow to 100 pounds and eat so much plankton, up to 40 percent of their body weight every day, that other species go hungry, according to Napoleon.  To stop the voracious eaters from entering the Great Lakes, the U.S. Army Corp of Engineers implemented a shocking plan.

Activated in 2002, electrified cables run across the bottom of the Chicago Sanitary and Ship Canal at a point between Lemont and Romeoville.  The carp find the charge in the water unpleasant, and the barrier has been successful in turning away the invaders.

Though specialists are conflicted about saying anything nice about Asian carp -- they far prefer that people dislike the fish -- there is an appetizing way citizens can help the fight against the invasive species.

"They taste really good," Charlebois said.