And waterborne transportation is not easily substituted for by land forms.  Aside from being the most economical form of transportation it is also the most capable of heavy lifts and sheer volume of cargo.

You don't unload a ship onto a train; you unload a ship's cargo onto multiple trains.  One barge may carry in excess of five hundred tons of grain; how many trucks are you going to need for that?

The $3 million fish kill required for the electric fence maintenance resulted in 90 tons of dead fish and yielded one dead carp.

The food these carp feed on, plankton, occurs largely in the shallower waters of the Great Lakes, lending further credence to their unsuitability for winter survival in those quick to freeze shallower waters.  The most likely effect they would have on the waters of the Great Lakes is to make them clearer.

The Chicago Ship and Sanitary Canal is responsible for in excess of $1 billion in shipping annually.  That's over 1 billion reasons to study the matter more thoroughly before panicking.