With a total land area of 97,914 square miles, Wyoming is home to 19,347 miles of streams, 427,219 acres of lakes and reservoirs, and an estimated 940,000 acres of wetlands.

The Continental Divide subdivides the state into four major drainage basins, including the Missouri, Columbia, Colorado and the Great Salt Lake basins. This geographic feature makes Wyoming the headwaters of the West. The headwaters of the Green River, a major tributary of the Colorado River, arise in the glaciers and snowpack of the Wind River Mountains.

More than 90 percent of the water flowing through Wyoming originates within the State. Less than 10 percent of Wyoming receives more water as precipitation than is lost back to the atmosphere through evaporation and transpiration.

Although Wyoming's portion of the Basin encompasses 16 percent of the land area in Wyoming (including the “Closed Basin” portion of the State in the Red Desert area), it is home to more than ten (10) percent (67,900 persons from the 2010 census) of the State's population. Communities served by Green River Basin water include Baggs, Pinedale, Big Piney, Farson, Kemmerer, Green River and Rock Springs. The largest Wyoming transbasin diversion of Colorado River system waters is into the over-appropriated North Platte River system. The City of Cheyenne diverts, on average, 10,664  acre-feet of water annually from the Little Snake River Basin to replace out-of-priority diversions of North Platte River Basin water used within Cheyenne.  In addition, the Broadbent Supply Ditch diverts water from Van Tassel Creek, tributary to the Green River, into the Bear River Drainage for 767 acres permitted for irrigation with Green River Basin water (recent year diversions have been about 370 acre-feet per year) and two other minor transbasin diversions divert water into the Sweetwater and North Platte River Basins for irrigation use.

In the Wind River Mountain Range, precipitation averages between 40 and 60 inches per year. The largest concentration of glaciers in the American Rocky Mountains occurs in the Wind River Range. Lower elevation portions of the Basin receive 7-9 inches per year. By comparison, annual precipitation across the entire state averages 14.5 inches.

The mean annual water balance (precipitation minus evapotranspiration) for the Green River Basin has a negative value. However, runoff, of which about 70 percent is derived from snowmelt, occurs during a period (spring/early summer) when the Basin has a positive water balance. Therefore, reservoir storage plays an important role for the Green River water supply during non-runoff months. The total reservoir storage capacity within Wyoming's portion of the Green River Basin is in excess of 4.4 million acre-feet.  Flaming Gorge Reservoir, situated on the Stateline between Wyoming and Utah, can store up to 3,790,000 acre-feet of water.  Further upstream, the State of Wyoming has contractually purchased 120,000 acre-feet of Fontenelle Dam storage (the reservoir can store up to 345,000 acre-feet of water) from the Bureau of Reclamation, ensuring the availability of water for Wyoming's agricultural, commercial, industrial, municipal and recreational needs both for the present and the foreseeable future.  Additional storage in the headwaters of the Green River Basin continues to be investigated and is needed for late-season, supplemental irrigation water use.

Wyoming's economic well-being revolves around three industries -- the extraction of minerals, tourism and recreation, plus agriculture, which is the largest user of water in the State (exceeding 80 percent of the total). The current “Green River Basin Plan” (December 2010) prepared as part of the State’s ongoing river basin water planning program, indicates that 334,500 acres are irrigated in the Basin. Alfalfa, native grasses and small grains are the predominate crops due to the short growing season and high elevation of the irrigated lands. Sparse rainfall means the Basin is generally arid and is thus agriculturally suitable only for grazing and livestock, unless irrigation water is continually supplied.

Millions visit Wyoming each year, flocking to the State's many spectacular and popular vacation and recreation attractions; many of these have a water component and are located within the Colorado River Basin. Water-based recreation plays a significant role in the economic base of the Basin. Flaming Gorge, Fontenelle, Fremont Lake, the Green River and the alpine biome areas of the Wind River Range support fishing, hunting, power boating, sailing, canoeing, rafting, skiing, hiking, mountaineering and wildlife observing. Wyoming has 22 species of game fish, including brook trout (char), brown trout, cutthroat trout, golden trout, kokanee salmon, and lake trout (char) that thrive in the clear and cold environment of the Basin's lakes and streams.

To help maintain existing stream environments and fisheries, the Wyoming Legislature enacted an instream flow law in 1986, making instream flow, provided either from natural stream flow or from storage water, a beneficial use of water. Between 1986 and December 2012, thirty-four instream flow applications in the Green River Basin were filed with the State Engineer's Office.  Two filings have been granted permits.

Construction of Fontenelle Dam induced changes in the Green River which Congress anticipated when it established the Seedskadee National Wildlife Refuge in 1965 to offset the loss of habitat due to the construction of Fontenelle and Flaming Gorge dams. The refuge was established on approximately 26,000 acres of sagebrush plains, cottonwood groves and marshes encompassing nearly thirty-seven (37) miles of the Green River.  The refuge provides habitat for such diverse species as pronghorn, shiras moose, trumpeter swans, sage grouse, raptors, pelicans and trophy trout.  Guests can visit historic Lombard Crossing which was used by emigrants traveling the Oregon, Mormon and California Trails.







Wyoming became the first state in the union to claim state ownership of water when the State Constitution became effective upon entering statehood in 1890. Wyoming's water law is based on the prior appropriation doctrine. Wyoming's first territorial engineer and state engineer, Elwood Mead (who became Commissioner of the U.S. Bureau of Reclamation in 1924 and for whom Lake Mead was named) was mainly responsible for writing Wyoming's water laws. It has not been found necessary to change much in those laws during the 125 years since the Territorial Engineer’s Office was established.   Wyoming's water laws have provided the basis for laws governing water appropriation and use in many other western states.

With an average elevation of 6,400 feet (second in the nation) and the Continental Divide parsing the state into four major drainage quadrants, Wyoming is a headwaters state.  Accordingly, Wyoming is a party to seven interstate compacts and two U.S. Supreme Court decrees which govern her rights to beneficially use water, including the Colorado River Compact of 1922 and the Upper Colorado River Compact of 1948, which apportioned 14 percent of the Upper Basin water supply to Wyoming’s users in perpetuity.


In a continuing effort to protect and properly manage Wyoming's water resources, the Wyoming Legislature authorized the Wyoming Water Development Commission (WWDC) to initiate a Basin Water Planning Process in 1999 to cover each of the seven major river basins in the state.  The primary objective of the process is to identify and document current and future uses of water within the state.  The initial Green River Basin Water Planning Process final report was completed in February 2001; as noted above, that plan was updated in December 2010  All of the basin reports completed may be obtained from the WWDC Water Planning Web Site (http://waterplan.state.wy.us/). 

Wyoming’s Current Depletions in the Green River Basin

(2010 in acre-feet)
Surface Water Resources (Normal Conditions) 2,381,316
     Irrigation 389,324
     Municipal, Domestic, & Stock 21,859
     Industrial 56,833
     Reservoir Evaporation 121,300
Surface Water Leaving the State 1,792,000

* Data provided by the Wyoming Water Development Office/Green River Basin Plan/Statewide Framework Water Plan