A Washington Post article details the lawsuit filed by the State of Michigan against Illinois to close off the water connection of the Chicago and Calumet Rivers to Lake Michigan.
The lawsuit also challenges Chicago's exemption from the Great Lakes Compact which allows the city to draw as much as 2 billion gallons of water from Lake Michigan, which then leaves the Great Lakes basin into the Mississippi River.
If Michigan is successful in its suit, it could possibly force not only the closure of the shipping channels and the end of barge traffic through the Cal-Sag channel, but could also force the city to re-reverse the direction of the Chicago River back toward Lake Michigan, entirely changing the water infrastructure of Chicago and nearby cities.