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Montana v. Wyoming

ELR Citation: 41 ELR 20168
Nos. No. 137, (U.S., 05/02/2011)

The U.S. Supreme Court held that Wyoming did not violate the Yellowstone River Compact by allowing its pre-1950 water appropriators to increase their net water consumption by improving the efficiency of their irrigation systems. The compact protects beneficial use water rights in existence prior to 1950 under the doctrine of appropriation. Montana alleged that the new irrigation systems use sprinklers that reduce the amount of wastewater returned to the river, thereby depriving Montana's downstream pre-1950 appropriators of water to which they are entitled. But the compact incorporates the ordinary doctrine of appropriation without significant qualification, and in Wyoming and Montana, that doctrine allows appropriators to improve their irrigation systems, even to the detriment of downstream appropriators. As such, more efficient irrigation systems are permissible under the compact so long as the conserved water is used to irrigate the same acreage watered in 1950. Montana's increased-efficiency allegation therefore fails to state a claim for breach of the compact. Thomas, J., delivered the opinion of the Court, in which Roberts, C.J., and Kennedy, Ginsburg, Breyer, Alito, and Sotomayor, JJ., joined. Scalia, J., filed a dissenting opinion. Kagan, J., took no part in the consideration or decision of the case.