A major reach of the Sand Hill River downstream of Fertile, Minn., was the subject of a flood control project constructed by the Corps of Engineers from 1955 to 1958. It involved straightening the river and constructing four drop structures and served as a drainage improvement to local agriculture. Overall, more than 18 miles of the Sand Hill River was straightened or abandoned. The straightened channel decreased channel length, increased channel grade, increased channel conveyance, and reduced the flood profiles in the lower Sand Hill River watershed. A series of four concrete drop structures were installed in the new Sand Hill River alignment to provide grade control. These grade control structures created six to eight-foot changes in bed grade, but left the river itself impassable for spawning fish. A preliminary restoration plan completed in 2003 recommended several measures to improve fish passage in the river including construction of rock structures at each of the Corps drop structures in the river as well as installation of several riffles and pools to decrease the slope of the river and create areas for refuge and rest for migrating fish.