The Supreme Court next week will wade into a dispute between Montana and Wyoming over water rights to two rivers that flow through both states.
Montana claims Wyoming farmers and industries are using too much water in a region where it remains a scarce resource.
At issue are the waters of the Powder and Tongue rivers, both tributaries of the Yellowstone River, which run into Montana from Wyoming.
Rights to the water have long been settled via the Yellowstone River Compact, which was finalized in 1951, but in 2007 Montana claimed that Wyoming had violated the agreement on several counts.
To be argued Monday, the case, Montana v. Wyoming and North Dakota, arises under the court's so-called original jurisdiction because it is a dispute between states -- meaning there is no lower court ruling for the justices to review.
Water law expert Kate Fox, a partner at the Davis & Cannon law firm in Cheyenne, Wyo., said the case can be viewed as the latest chapter in the ongoing struggle between Wyoming and surrounding states over water.
Other states, including Montana, "want to have their fair share of the water that Wyoming thinks it has a right to," she said.
Wyoming's starting position, Fox said, can be summarized as: "All those greedy bastards downriver want to take our water."
Montana alleged that coalbed methane production has led to increased pumping of groundwater and that modern irrigation techniques had used more of the rivers' waters.
North Dakota is a party in the case because it is also a signatory of the compact, but is not directly implicated in the dispute between the two other states and has not taken an active role.
The Supreme Court, as is common in such cases, appointed a special master -- Barton Thompson, a Stanford Law School professor -- to handle the case.
Thompson recommended in a February 2010 report that the court deny Wyoming's motion to dismiss and grant partial summary judgment to Montana. He rejected Wyoming's contention that Montana could not sue because the compact did not cover any uses of water in Wyoming that were already recognized before the agreement was signed.
Thompson subsequently found that increased consumption of that water in Wyoming as a result of modern irrigation did not violate the agreement but concluded that the pumping of groundwater could constitute a violation. The Supreme Court will examine Montana's objection to the first conclusion.
"Although Wyoming has historically disputed its obligations under the compact, court officials have generally sided with Montana," Montana Attorney General Steve Bullock said in a statement. "On this one remaining issue, we believe that Wyoming -- in violation of the compact -- is taking water from Montana users who have long-standing rights."
Bullock, a Democrat elected in 2008, will argue the case himself. He wrote in the state's brief that Thompson had "misunderstood the nature of Montana's claim and disregarded the compact's plain language."
In response, Wyoming Attorney General Bruce Salzburg, who was appointed by Gov. Dave Freudenthal (D) in 2007, wrote in his state's brief that the compact does not limit the amount of water that can be used for irrigation.
"Wyoming irrigators with pre-1950 water rights may increase water consumption by their crops by adopting sprinkler irrigation technology without creating any Wyoming liability under the compact," Salzburg said.
Justice Elena Kagan has recused herself, likely due to her previous role as solicitor general. The federal government is not a party to the case, but the Obama administration filed an amicus brief supporting the special master's findings.
Acting Solicitor General Neal Katyal wrote that there is nothing in the compact to suggest that water rights "be limited to the amount of water that was actually consumed by crops in 1950."
Whatever ruling the Supreme Court issues is unlikely to end the dispute, as there remain other issues to be argued before the special master, including how to resolve Montana's complaint about the use of groundwater for coalbed methane production.
Anadarko Petroleum Corp., one of the main companies involved in methane production in Wyoming, unsuccessfully sought to intervene in the case to defend its interests on that point.
Click here to read the special master's report.