This committee began its two-year study late in 1999. Five meetings were held along the river: Bismarck, North Dakota; Columbia, Missouri; Great Falls, Montana; Omaha, Nebraska; and Pierre, South Dakota (a sixth meeting was held at the National Academies’ Beckman Center in Irvine, California, in February 2001). The committee spoke with federal and state scientists and engineers, representatives from Indian tribes, experts on Missouri River institutions and policies, groups interested in Missouri River ecology and river management, the commercial navigation industry, and many citizens.

This report focuses on the Missouri River ecosystem. However, an understanding of the larger context of water resources development is helpful in explaining some of the patterns reflected across the Missouri basin. Namely, changing values and water management policies in the United States are part of a larger global shift in which assumptions about the benefits of dams and the ability to appropriately distribute those benefits are being rethought.

The rivers of the United States underwent considerable hydrologic and ecological changes during the twentieth century. The most obvious of these changes was the inundation of extensive stretches of these rivers behind dams. The twentieth century saw the Corps of Engineers and the Bureau of Reclamation, along with local, state, and private entities, construct hundreds of dams and greatly increase water storage. For example, in a given year, 60 percent of the United States’ entire river flow can be stored behind dams (Hirsch et al., 1990). Dams in the Missouri River basin have the capacity to hold roughly 106 million acre-feet of water, with the six Corps of Engineers Missouri mainstem reservoirs having a combined capacity of roughly 73.4 million acre-feet, making it North America’s largest reservoir system (USACE, 2001). The waters stored by these reservoirs are intended to serve multiple purposes, including irrigation, recreation, and controlled releases for navigation enhancement. The reservoirs are also operated so