The U.S. Supreme Court sided with Wyoming farmers Monday in a water lawsuit that claimed they were taking too much water from a river system shared with neighboring Montana.
The high court struck down one of four claims made by Montana in a 2007 complaint that said Wyoming was violating a 1950 agreement by depleting water from the Tongue and Powder rivers.
Montana had contended that more efficient irrigation techniques in Wyoming have been sucking the rivers dry and keeping run-off from flowing downstream. But in a 7-1 decision, justices said more efficient irrigation was permissible under an agreement known as the Yellowstone Compact even if it comes at the detriment of downstream users.
Left unresolved following Monday's ruling was the broader question of whether Montana is getting its fair share from the rivers as Wyoming builds new reservoirs, the amount of water used by the oil and gas industry increases and farms expand. Attorneys now turn their attention to calculating how much water is being used _ a process expected to take many months.
Justice Clarence Thomas wrote Monday's decision.
It centered on modern irrigation systems that use sprinklers to allow farmers to increase crop yields by applying water directly to crops, rather than flooding entire fields. In the case of the Tongue and Powder rivers, that means less water left over to run downstream into Montana.
But justices determined Montana's loss does not mean Wyoming is doing anything wrong. Thomas compared improved irrigation methods with farmers who recapture water so it can be used more than once _ a practice that has been upheld by the Montana Supreme Court.
"By using sprinklers rather than flood irrigation, those water users effectively recapture water," Thomas wrote. "They are simply different mechanisms for increasing the volume of water available to the crops, without changing the amount of diversion."
Wyoming Deputy Attorney General Pete Michael said the ruling resolved an important issue, by putting to rest at least one aspect of a case that could threaten the state's agriculture and energy industries if it ultimately goes in Montana's favor.
Although river levels are expected to be high this year following heavy winter snows, the struggle over the region's scarce water supplies will continue, Michael said.
"The test comes in dry years. That's when the system gets pushed," he said.
Justice Antonin Scalia was the only dissenting vote. Justice Elena Kagan did not participate in the case because she worked on it while in the solicitor general's office.
Scalia wrote in his dissent that Montana was merely trying to protect its rights under the 1950 agreement _ not seeking a precise volume of water every year. The question is not how much water is diverted from the rivers but how much is depleted from the overall water supply, Scalia wrote.
He added that his colleagues disregarded the text of 1950 agreement and instead substituted their own "none-too-confident reading" of common law.
Montana Attorney General Steve Bullock had argued the case before the high court in January. Assistant Attorney General Jennifer Anders said Monday it was "hard not to be disappointed" with Monday's ruling but said it needed to be put in perspective.
"We brought four claims, and the Court is allowing three of those claims to move forward," she said. ". "Our objective in bringing this lawsuit was to protect Montana water users and to fairly administer the agreement between our state and Wyoming. Even with today's decision, we will reach those goals."
A court-appointed special master had rejected part of Montana's claim last year. Stanford University law professor Barton Thompson Jr. agreed with Wyoming attorneys who argued that the case came down to how much water was being taken out of the Tongue and Powder rivers, not what happens to the water after that.
In October, the court ruled that Montana has raised a valid issue with its lawsuit and rejected Wyoming's attempt to dismiss the case.
Remaining aspects of the lawsuit could have consequences for Wyoming's natural gas industry. Over the last decade, companies seeking a type of gas known as coal-bed methane have pumped billions of gallons of water from underground aquifers shared by the two states.
Montana contends the companies are draining water that would otherwise feed the Tongue and Powder rivers. A Texas-based energy company, Anadarko Petroleum Corp., attempted to intervene in the case but was denied.
North Dakota is also listed as a defendant because it is a party to the Yellowstone Compact. However, no claims have been made against it and the outcome of the lawsuit is likely to have little bearing on the state.
The case is Montana v. Wyoming and North Dakota, 137, Orig.
Associated Press writer Jesse J. Holland contributed to this story from Washington.