Before Offutt's flatboat could reach the Illinois River, it got hung up on a milldam at the Old Sangamon town.
From the en.wikipedia.org
Rather than tear down the whole milldam and radically change the surrounding ecosystem, the researchers recommend river restorers only remove part of it.
From the sciencedaily.com
More examples
Dam to make a millpond to provide power for a water mill
A milldam is a dam constructed on a waterway to create a mill pond.
To dream that you see clear water pouring over a mill-dam, foretells pleasant enterprises, either of a business or social nature. If the water is muddy or impure, you will meet with losses, and troubles will arise where pleasure was anticipated. ...