Interstate Compacts and Decrees
As a headwaters state, Wyoming is party to seven interstate compacts and 2 U.S. Supreme Court decrees. In addition to participating in the Commissions that have been established to administer these compacts, the State Engineer also participates in a number of basin- or region-wide water resource groups and associations.
North Platte River, 1945 -- The Supreme Court ruled that Wyoming could irrigate up to 168,000 acres. Natural flow split at the state line 25% to Wyoming and 75% to Nebraska.
Laramie River, 1911, 1922 -- Allows Colorado to divert up to 39,750 acre feet per year.
Teton Creek and South Leigh Creek ("Roxanna" Decree), 1941 -- When the flow naturally available at the state line in either stream declines below specified thresholds, it is split between Wyoming and Idaho apportionment diversions.
Colorado River Compact, 1922 -- Divides the basin at Lee Ferry, AZ. Provides that the upper basin states may use 7.5 million acre feet annually.
Upper Colorado River, 1948 -- Apportions 14% of the water allocated in the Colorado River Compact to Wyoming.
Amended Bear River, 1978 -- Provides for administration of flows and storage between Utah, Idaho, and Wyoming.
Belle Fourche River, 1943 -- Allocates new uses after 1943, 10% to Wyoming and 90% to South Dakota.
Snake River, 1949 -- Wyoming may divert 4% of the ID-WY stateline flow for post-1949 uses.
Upper Niobrara River, 1962 -- Restrictions on storage in larger (over 500 acre feet) facilities.
Yellowstone River Compact, 1950 -- Allocates the flows of the Powder, Tongue, Bighorn and Clarks Fork Rivers between Montana and Wyoming.