Thursday, June 11, 2009

Time to undo artificial connection between the Great Lakes and the Mississippi River basin?

Time to undo artificial connection between the Great Lakes and the Mississippi River basin?

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It's ironic that the Prairie State is bordered by two of the world’s most extensive aquatic systems. On the northeast we’ve got Lake Michigan, the fifth largest lake in the world and our connection to the rest of the Great Lakes system and by extension the Atlantic Ocean. On the west we’re bordered by the Mississippi River, which, with all of its tributaries, drains nearly half of the continental United States. Indeed, except for a tiny sliver of Lake Michigan shoreline, the whole of Illinois lies within the Mississippi drainage, since all of the other waters that flow from the state wind up in the Big Muddy.

Prior to the year 1900, these two colossal systems were nowhere directly connected. They came very close to one another in an area of what is now the southwest suburbs of Chicago. There, the upper Des Plaines River, which is part of the Mississippi drainage, and the West Branch of the Chicago River, which then flowed into Lake Michigan, were separated only by a slim drainage divide, known as the Chicago Portage. But because there was this land divide, however narrow, fish and other aquatic organisms were unable to easily pass back and forth between the Great Lakes and the Mississippi River systems.

The land barrier between the two systems was breached in 1900 by completion of the Chicago Sanitary and Ship Canal, which famously reversed the flow of the Chicago River and enabled the City to flush its waste into the Mississippi basin rather than Lake Michigan. The extensive Chicago Waterway System still serves that function. In addition, it supports significant recreational boating and commercial shipping.

These functions notwithstanding, hindsight allows us to see that connecting the Mississippi Basin with the Great Lakes system so directly was not a good idea, either from an ecological or a financial perspective. That’s because doing so enables aquatic invasive species to move between them.

To date the most notorious invaders to make the passage from Lake Michigan into the Mississippi basin have been two small but prolific organisms, a fish called the round goby, and the better known zebra mussel. Both of these creatures cause irreparable harm to ecosystems where they are introduced, and control measures for zebra mussels alone cost millions of dollars annually.

Two species of invasive carp moving in the other direction—from the Mississippi toward the Great Lakes—have caused even greater concern in recent years, enough to generate action. The first line of defense against the movement of these invasive carp into Lake Michigan is an experimental electric barrier that has been operating in the Chicago Sanitary and Ship Canal since 2002. The next step will be the long-anticipated completion of a more permanent electric barrier, which should be fully operational sometime in the near term.

Beyond that, however, a broad coalition of groups interested in the health of aquatic ecosystems has begun to call for the establishment of a more substantial ecological separation between the Mississippi and the Great Lakes ecosystems. In a report released late last year [] the Alliance for the Great Lakes outlines six options for separating the two watersheds to prevent the transfer of invasive species between them. None of these solutions is easy or cheap. But in the long run, the financial and ecological costs of pursuing half-measures would be even greater.