Groups representing states and cities in the Great Lakes region have drafted a plan to separate the lakes from the Mississippi River watershed in the Chicago area.
The backers describe the plan as the only sure way to protect both aquatic systems from invasions by destructive species such as Asian carp.
The plan has an estimated cost of up to $9.5 billion US and centres on two drainage basins constructed more than a century ago.
Scientists say they are the likeliest route for menacing carp to reach the lakes, where they could destabilize food webs and threaten a valuable fishing industry.
Tim Eder, director of the Great Lakes Commission, says the Great Lakes have "suffered immensely because of invasive species" and "we have to put a stop to this."
The US Army Corps of Engineers is already conducting its own study of how to close 18 potential pathways between the two systems, including the Chicago waterways.
The corps plans to release its findings in late 2015.