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Reservoirs play imperative role in Mont v. Wyo

by Wyoming Livestock Roundup

Cheyenne – At the Wyoming Water and Energy Law Conference in Cheyenne on June 12-13, Attorney General Peter Michael summarized and reported a litigation update on the Montana v. Wyoming water case. 

This landmark case argues the appropriation of interstate water rights issue arising from the 1950 Yellowstone River Compact between Wyoming and Montana. 

In 2007, Montana filed suit against Wyoming for not appropriating enough water from the Tongue and Powder Rivers to go to Montana. 

The trial phase of the case ended at the beginning of May, and both sides are awaiting the report from the U.S. Supreme Court-appointed Special Master  Baron Thompson. Thompson is a professor at Stanford Law School. 

The report is expected to be released in July, and both Montana and Wyoming will have a chance to object to the report. If either side does object to the report, the case will then be argued before the U.S. Supreme Court. 

“This case is about how the doctrine of appropriation works across two states,” said Michael. 

Michael further mentioned the biggest issue with the case now is determining what role reservoirs play with interstate water law. 

“There is interesting discussion about how a reservoir interacts with the doctrine of appropriation and if a reservoir can be filled twice and takeover a river system,” he comments. “The answer to that is no.” 

Michael adds, “One of the biggest issues of this case is Montana has passed so much water through their reservoirs in the winter, for various reasons, that they do not have enough water to use in the spring.” 

He further explains that Montana has a history, even in 2002 and 2004 when they called on Wyoming for water, of letting too much water pass through their reservoirs. Some estimates have been made that Montana let enough water through their reservoirs that they could have been filled up to their entirety. 

Madeline Robinson is editor of Wyoming Livestock Roundup. Comments about this article can be submitted to

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