Holding: Original; Montana has failed to state a claim for breach of the Yellowstone River Compact. Wyoming's more efficient irrigation systems are permissible under the Compact as long as the water conserved by those systems is used to irrigate the same acreage watered in 1950. (Kagan, J., recused).
Plain English Holding: Wyoming did not violate the Yellowstone River Compact by allowing Wyoming residents to implement more efficient irrigation systems on the farmland that existed when the compact was signed, even though the result is less water flowing downstream to Montana.
Judgment: Montanaâ€™s exception to the report of the Special Master is overruled., 7-1, in an opinion by Justice Thomas on May 2, 2011. Justice Scalia filed a dissenting opinion. (Kagan, J., recused).