State of Montana v. State of Wyoming, 131 S. Ct. 1765 (U.S. Sup. Ct. 2011)

(Article V(A) of the Yellowstone River Compact of 1951 incorporates ordinary doctrine of appropriation without significant qualification; as doctrine applied in Montana and Wyoming appropriators can improve their irrigation systems to detriment of downstream appropriators; Montana's challenge to Wyoming's more efficient sprinkler irrigation process (to which pre-1950 users may switch) not challengeable even though increased consumption in Wyoming deprived Montana of typical water allotment; Compact did not guarantee Montana set amount of water).