Originally intended to prevent waste from polluting the city's drinking water, the Chicago Sanitary and Ship Canal reversed the flow of the Chicago River a century ago, diverting it from its natural course which empties into Lake Michigan, and sending it instead towards the Mississippi River.
Almost from the outset, the project was plagued by controversy. Downstream communities complained of having to deal with Chicago's sewage, while members of the Great Lakes region worried that the reversal of flow, combined with Chicago's enormous withdrawal of water for other municipal purposes, would slowly drain the Lakes. The Missouri Attorney General filed a suit during the canal's construction asking the U.S. Supreme Court for a permanent injunction against its operation, however, the canal opened before any action could be taken, leading to a litigious battle that continues today.
While the amount of water withdrawn from Lake Michigan remains a major concern, today the canal is at the center of a new storm. When the course of the Chicago River was altered, it connected two watersheds, those of the Great Lakes and the Mississippi River, which had previously been isolated from one another. This allows aquatic species which should be separated to travel freely between the two ecosystems.
While this connection poses relatively little problem among native species, several species of Asian carp
, a non-native fish originally imported for algae control and aquaculture, have been introduced into the Mississippi watershed. These fish, which were released from commercial ponds by flood waters in the early 1990s, have adapted so successfully to their new habitat that they are now firmly established and are spreading at a rate of about 50 miles per year, making their arrival to Lake Michigan imminent.
The carps' voracious appetite, which made them prized cleaners in aquaculture ponds, makes them a danger to the Great Lakes. Weighing up to 100 pounds, they are capable of consuming an amount nearly equal to their body weight each day. Combine this with their rapid growth and prolific reproduction, and the invasive carp are poised to out-compete native fish species, potentially depleting plankton and other small organisms which form the base of the Great Lakes' food web. At stake is not just the welfare of the ecosystem, but also the future of the Great Lakes' $7 billion fishing industry which depends on a stable food web and open spawning grounds.
With the Chicago Sanitary and Ship Canal serving as the only link between the Mississippi and the Great Lakes watersheds, it has become the focal point of efforts to prevent the spread of carp into the Lakes. Several methods have been considered, including the introduction of electrical barriers which pulse a non-lethal current though the canal, deterring fish from passing. There are currently three such barriers in place, two of which are operational with the third expected to come on-line in 2010.
Despite these measures, the DNA of two Asian carp species has been found upstream of the barriers, leading biologists to fear that the fish are already closer to Lake Michigan than expected. A massive kill along a six mile stretch of the canal, intended to prevent fish from passing the electrical barriers while they were disabled for maintenance, also produced evidence for the fishes' advance.
Because of the enormous threat that Asian carp pose to the Great Lakes, these findings have revived the legal battle which began upon the canal's inception. Last week Mike Cox, Michigan's attorney general, filed a lawsuit again asking the U.S. Supreme Court for an injunction against the canal's operation. "With DNA within six miles of Lake Michigan, now is the time to do it," Cox said during a recent press conference.
Emergency efforts to stop the carps' progression, including the poisoning of large stretches of waterway and the strategic release of water through sluice gates, are now being considered, but closure of the canal and separation of the watersheds may be the only decisive means of preventing the carp from reaching Lake Michigan.
While some downplay the danger of invasive species, the threat which Asian carp pose to the Great Lakes is very real. Their introduction could forever alter both the economy and the ecology of these valuable waters. Hopefully the catastrophe of the Asian carp will be a wake-up call, encouraging states to reconsider aging infrastructure. Marvels which solved the problems of our forefathers, may pose new and expected challenges in today's changing environment.