Portions of the High Plains were not settled until the early 20th century because irrigation water was needed. In response to pressure for Western settlement, Congress created the Reclamation Service in 1902 to develop water resources and make cultivation possible on land considered desert wasteland. In the Wind River Basin, the Bureau of Reclamation undertook the Riverton Project in 1920. Its Midvale Irrigation District includes 73,000 acres, three dams—Bull Lake Dam to the south and Diversion Dam and Pilot Butte Dam to the east—100 miles of canals, and 300 miles of laterals. Completed in 1923, Diversion Dam diverts water from the Wind River to the Wyoming Canal and was the first dam in the nation with a road incorporated into its structure and the first to contain a fish ladder. Historian T.A. Larson called the Riverton irrigation project "a perennial object lesson in the formidable difficulties inherent in large-scale reclamation projects in the West." What began with financial and engineering problems also came to involve legal and political issues. As Native American self-determination rose, the Arapaho and Shoshone tribes exercised their right to Wind River water under an 1868 treaty, and court battles followed over water used to irrigate land opened to homesteading by Congress in 1905. The struggle underscored the importance of water in the West.