Dividing the waters: The case for hydrologic separation of the North American Great Lakes and Mississippi River Basins

Legislation has been introduced this year in the U.S. Congress, but not yet enacted, that would direct the U.S. Army Corps of Engineers to complete a study of the options that would prevent the spread of aquatic nuisance species between the Great Lakes and Mississippi River Basins. Hydrologic separation is the only option which closes the aquatic connection between the two basins and does not require continuous operation and maintenance of various technologies that have some risk of failure. The one-time, capital cost to separate the two basins is widely acknowledged to be high, and the outstanding question is whether the costs are justified given the significant risk of future ecological damages and long-term economic losses. Interests opposing separation have mounted a public campaign that the news media have picked up to deny that hydrologic separation should be considered or that a problem even exists. The campaign rests on four assertions: (1) existing electric barriers in the Chicago canals are effective; (2) it is too late--the carps are already in the Great Lakes or soon will be; (3) Asian carps will not thrive in the Great Lakes due to inadequate food and spawning habitat; and (4) Asian carps are unlikely to cause serious harm. Our review of these assertions and the ecological and socio-economic threats to both basins supports our recommendation that the pending legislation be passed and that it include analysis of hydrologic separation of the two basins.