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.

Court Decrees

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.

Interstate Compacts

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.