Restoring the Natural Divide Between Great Lakes & Mississippi River Basins

Strategies for restoring the natural divide between the Great Lakes and Mississippi River basins to keep Asian carp out of the Great Lakes – and, in the process, modernizing the Chicago Area Waterway System (CAWS) – are identified in a report by the Great Lakes Commission and the Great Lakes and St. Lawrence Cities Initiative. 

The three separation alternatives include a down-river single barrier between the confluence of the Chicago Sanitary and Ship Canal and the Cal-Sag Channel and the Lockport Lock; a mid-system alternative of four barriers on CAWS branches between Lockport and Lake Michigan; and a near-lake alternative of up to five barriers closest to the lakeshore. All three include measures to improve the CAWS’s role in flood management, wastewater treatment and maritime transportation, as well as stopping the inter-basin movement of aquatic invasive species.

The three separation alternatives in the report were developed by the engineering firm HDR, Inc., which considered some 20 possible barrier locations in its analysis. No recommended alternative is identified. However, one alternative, the mid-system solution, is the least costly and offers other advantages.

According to the report’s economic analysis, the cost of the barriers themselves is as low as $109 million. The addition of all improvements to address water quality, flood prevention and transportation brings the cost to between $3.2 billion and $9.5 billion, depending on the location and the degree to which the wastewater treatment plants on the system are improved to meet future Clean Water Act requirements.

The analysis also finds that households in the Great Lakes basin would have to be willing to pay, on average, about $1 a month from now through 2059 to cover the cost of the mid-system alternative, based on a projected cost of $4.27 billion. The Great Lakes Commission and the Cities Initiative point out that the construction costs to build the current CAWS in today’s dollars would be $11 billion.

The Great Lakes Commission, representing the eight Great Lakes states plus the Canadian provinces of Ontario and Québec, and the Cities Initiative, a coalition of U.S. and Canadian mayors, embarked on the accelerated study in 2010 believing separation to be the best strategy for preventing the movement of Asian carp and other aquatic invasive species between the two watersheds via the CAWS. The $2 million project was funded by a collaboration of six regional funders: the Joyce Foundation, C.S. Mott Foundation, Great Lakes Fishery Trust, Wege Foundation, Great Lakes Protection Fund and Frey Foundation.

To provide guidance and input for the project, a bipartisan Executive Committee was established and a diverse Advisory Committee was convened among stakeholders from the Great Lakes region, with an emphasis on interest groups in the Chicago area. In addition, a Resource Group made up of governmental and quasi-governmental entities with a direct interest in the project also participated.

The report and all supporting materials are available at