Belle Fourche River Compact, 1943
The Belle Fourche River begins in southwestern Campbell county and flows northeast to Moorcroft and into Keyhole Reservoir. After the river leaves Keyhole Reservoir it continues northeast around the Black Hills and just before hitting Montana takes a sharp southeast turn into South Dakota and exits the state.
The compact allows for Wyoming to use unlimited amounts of water from the river for small stock ponds (less than 20 acre feet in capacity). The compact also allocates Wyoming 10% of the rivers unallocated flow to use in Wyoming.
Colorado River Compact, 1922 and 1948
The Colorado River begins in central Colorado and flows west into Utah. It then flows south into Arizona then west and forms Arizona’s western border with Nevada and California till it exits the United States. Wyoming’s shares in this system are the Green River which begins in western Wyoming and flows south into Utah, and the Little Snake River which begins on the Wyoming-Colorado border and flows west crossing the border many times before heading south into the Yampa River (a tributary of the Green River).
There are two separate compacts that dictate Wyoming’s use of its Colorado river water. The 1922 Compact allows for the upper Colorado river basin states (Wyoming, Colorado, Utah, and New Mexico) to use 7.5 million acre feet of water per year, but must also deliver 75 million acre feet over any ten year period of water to the lower basin states (California, Nevada, and Arizona). The Upper Basin Compact of 1948 states that of the volume allocated to the upper basin states, Wyoming is entitled to 14% of the total water left over after the lower basin states get their full amount. In addition, Wyoming is entitled to 50% of the water in the Little Snake River below its confluence with Savery Creek in excess of the lower basin requirements.
Upper Niobrara River Compact, 1962
The Niobrara River begins in the central part of Wyoming’s eastern border with Nebraska. Starting in western Niobrara County and heading due east till it joins the Missouri river in northeastern Nebraska.
The compact allows for unlimited use of water for 20 acre foot stock tanks, and unlimited use of the river west of its confluence with Van Tassel Creek. Water and storage east of Van Tassel Creek is based on priority of interstate water rights.
Snake River Compact, 1949
The Snake River begins in Teton County section of Yellowstone National Park and flows south into northern Lincoln County where it turns west into Idaho. The river then flows west across Idaho and follows Idaho’s western border north into Washington and heads west from there where it meets the Columbia River and flows into the Pacific Ocean. This compact includes the waters of the Salt River and the Greys River which flow northward in Lincoln county and meet the Snake River near its exit into Idaho.
The Snake river compact allows for unlimited stock water reservoirs of 20 acre feet or less and 4% of the water, including the Salt and Greys Rivers, to be used in Wyoming.
Yellowstone River Compact, 1950
The Yellowstone River begins in the Absaroka Mountains of Park County and flows north into Yellowstone Lake. From the lake the river flows north into Montana then turns east and flows the entire distance of Montana to its eastern border with North Dakota where it flows into the Missouri River. The Yellowstone River has several major tributaries that flow out of Wyoming and meet the Yellowstone River in Montana. These major rivers are the Clarks Fork River, the Bighorn River, the Tongue River, and the Powder River.
The compact exempts stock reservoirs of 20 acre-feet or less. Water rights with a date before 1/1/1950 are maintained, and regulation and control devices are exempted from the compact. The unappropriated flows of the Yellowstone’s tributaries are allotted as percentages per river. The Clarks Fork River flow goes 60% to Wyoming and 40% to Montana. Unappropriated flow from the Bighorn River is allotted 80% to Wyoming and 20% to Montana. From the Tongue River Wyoming gets 40% and Montana 60%. Lastly the Powder river is divided 42% to Wyoming and 58% to Montana. The actual Yellowstone River as it flows from Wyoming is not available for the state’s use because it begins in a National Forest and flows out of the state through the National Park in which water is not able to be diverted.
Wyoming’s Compacts, Treaties and Court Decrees By Interstate Streams Division, Wyoming State Engineer’s Office 2006, http://seo.state.wy.us
A History of Water Law, Water Rights and Water Development in Wyoming Craig Cooper, Cooper Consulting, June 2004, Wyoming State Engineer’s Office