U.S. Army Corps of Engineers: Information on the Navigation and Ecosystem Sustainability Program [open pdf - 1MB]
From the Document: "The Upper Mississippi River system provides approximately $1 billion in annual benefits to the nation's economy through boating, fishing, and other uses, according to the U.S. Army Corps of Engineers (Corps). The river system also supports irreplaceable habitats and ecosystems-- including more than 2.5 million acres of aquatic, wetland, forest, grassland, and agricultural habitats across the states of Illinois, Iowa, Minnesota, Missouri, and Wisconsin. In 1986, Congress declared its intent to recognize the Upper Mississippi River system as a nationally significant commercial navigation system and a nationally significant ecosystem. The Corps is responsible for operating and maintaining the navigation infrastructure along the Upper Mississippi River system and for managing, restoring, and protecting the surrounding ecosystem. According to the Corps, balancing the navigational importance of the river system with the need to protect the ecosystem is challenging. The Corps operates 37 lock and dam sites and maintains 1,200 miles of 9-foot deep navigation channels along the Upper Mississippi River and the Illinois Waterway, which connects with the Mississippi River and lies within the Upper Mississippi River basin."
Government Accountability Office: https://www.gao.gov/