Interstate and Federal Law
Lake Powell, which sits on the Utah-Arizona border, is the upper basin’s largest reservoir on the Colorado River. Water from Colorado River Storage Project reservoirs, including the Aspinall Unit in Colorado, is released to flow down to Powell where it is further regulated to ensure the terms of the Colorado River Compact are met.
Interstate Compacts, Equitable Kansas. International treaties with Mexico also affect Colorado’s water use. Apportionment Decrees and The unbridled ability of states to Treaties Colorado is a headwaters state, where four major rivers begin—the Colorado, Arkansas, Platte, and Rio Grande— supplying water to 18 downstream states and Mexico. However, Colorado must live within its water constraints. The first and most basic constraint on water use within the state is the amount of rainfall and snowfall that occurs each year. The second constraint is legal: Colorado has obligations to limit its uses and deliver water to downstream states under interstate water compacts and U.S. Supreme Court equitable apportionment decrees. Meeting these obligations can be viewed as Colorado’s top water right administrative priority. Failure to meet the terms of the Arkansas River Compact, for example, resulted in expensive litigation and a 2005 ruling that Colorado pay $34 million to ECOFLIGHT
allocate and govern water use within their borders halted early in the 20th century. In 1907, the Supreme Court in Kansas v. Colorado held that all states sharing a stream system were entitled to an equitable share of river water.
Under equitable apportionment, the U.S. Supreme Court has authority to allocate a state’s share of river water from time to time based on another state’s need, if a state files directly with the high court. The compact clause of the U.S. Constitution allows states to fix their allocations in perpetuity by contract, with congressional approval. An
Interstate Compacts, Treaties, Equitable Apportionment Decrees Colorado River Compact, 1922
Animas-La Plata Project Compact, 1968
La Plata River Compact, 1922
U.S.–Mexico Water Treaty, 1906
South Platte River Compact, 1923
U.S.–Mexico Rio Grande, Colorado, and Tijuana Treaty, 1944
Rio Grande River Compact, 1938
Wyoming v. Colorado, 1922
Republican River Compact, 1942
Nebraska v. Wyoming, 1945
Arkansas River Compact, 1948 Upper Colorado River Compact, 1948
Colorado v. New Mexico, 1984
Amended Costilla Compact, 1963
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