Business and transportation in the United States would be a lot more difficult with locks to even out heights between different bodies of water. Here is a 50 second time lapse video of the first ship of the spring passing through the locks of Sault Ste. Marie, Michigan.

Water traffic within the United States might not garner much attention compared to rail and truck traffic (perhaps except during seasons of drought) but it still accounts for a lot of goods and has a historic role in opening up the interior of the United States. For example, the connection between the Great Lakes and the Mississippi River through a canal and several rivers was critical in leading to the growth of Chicago.