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Interstate Water Management Committee Meeting Summary: March 23, 2023 — “MT v WY”

Link to recording: https://youtu.be/hFfam2PVlWE


  1. Call to Order – Drew Dehoff, SRBC; Chair
  2. Introductions of participants – Beth Callaway – ICWP Executive Director, Adel Abdallah, Beth Brown, Curt Sebastian, Drew Dehoff, Faith Sternlieb, Isabella Peterson, Jason Oyler, JB, Jen Verleger, Jennifer Zygmunt, Kay Whittington, Kirsten Wallace, Luigi Romolo, Mel Fegler, Pooja Kanwar, Steven Domber, Wei Han, Abby Ebach, Erin Fanning, Joy Loughry, Mabel Jones, Michael Weller, Michael Weller, Wes Cattoor.
  3. Interstate Litigation Webinar Series Presentation: “MT v WY” by Chris Brown, Wyoming Attorney General’s Office

In 2007, Montana alleged Wyoming violated the Yellowstone River Compact in the Tongue and Powder River Basins. U.S. Supreme Court appointed Special Master Barton H. Thompson, Jr., a law professor at Stanford Law School. Special Master’s Website: http://www.stanford.edu/dept/law/mvn/. This website contains PDFs of everything filed with the Special Master.

Yellowstone River Compact – The Compact governs interstate use of the Clarks Fork, Wind/Big Horn, Tongue, and Powder Rivers. Took effect January 1, 1950. Lawsuit involves Article V: Article V(A) relates to pre-1950 water rights; Article V(B) discusses: 1) supplemental water supplies for existing rights, and 2) allocations of unused and unappropriated waters.

Montana’s Bill of Complaint – Montana claimed that Wyoming violated the Compact by:

  • Refusing to curtail its consumption of water beyond the amounts consumed in 1950 whenever the amount necessary for Montana’s pre-1950 rights is not passing the state line.
  • Allowing new and expanded water storage facilities. Allowing new acreage to be put under irrigation. Allowing groundwater pumping associated with coalbed methane production.
  • Allowing pre-1950 water rights to increase their consumption.

Yellowstone River Compact – Article V(A)

“Appropriative rights to the beneficial uses of the water of the Yellowstone River System existing in each signatory State as of January 1, 1950, shall continue to be enjoyed in accordance with the laws governing the acquisition and use of water under the doctrine of appropriation.”

Main Trial Issues –

  • Whether Montana made a call when it was receiving insufficient water to enjoy its pre-1950 rights;
  • Whether Montana did not receive sufficient water to enjoy its pre-1950 rights;
  • Whether Wyoming allowed post-1950 storage or use of water while Montana was suffering a pre-1950 shortage; and
  • Whether Wyoming’s post-1950 storage or use reduced the amount of water available to Montana at the Stateline of the Tongue River between Wyoming and Montana.

The Call – The doctrine of appropriation “requires senior appropriators to notify junior appropriators when they are short of water if they wish junior appropriators to reduce their diversions –an action known as ‘calling the river.’” Wyoming conceded early on that Montana made a call for water in both 2004 and 2006.

Montana sent “call” letters to Wyoming in both 2004 and 2006. For 2006, the Special Master found that the date of Montana’s call was the date of its letter, or July 28. For 2004, even though Montana sent a “call” letter on May 18, the Special Master found that Montana made an earlier call during an April 14 meeting of the Compact Commission’s Technical Committee. Montana asked Wyoming how it would respond “if” Montana made a call for post-1950 storage in Wyoming, and told Wyoming it would send a “letter stating our concerns and needs.”

Special Master Conclusions

  • The Special Master recommended that the Supreme Court find Wyoming not liable for violating the Compact for thirteen of the fifteen years claimed by Montana.
  • He concluded that Wyoming violated the Compact in 2004 and 2006 by diverting and/or storing water under post-1950 rights after Montana made a call.
  • After making adjustments for conveyance losses to the Stateline, he recommended that the Supreme Court find Wyoming liable to Montana in the amount of 1,300 acre feet for 2004, and 56 acre feet for 2006.

Special Master’s Final Report

  • During 2017, Montana and Wyoming conferred with regard to the content of a Decree which would incorporate the legal rulings in the case. The states were unable to reach agreement on Decree provisions.
  • Special Master held hearing on May 1, 2017, regarding the contents of a decree. States commented on a draft proposed decree.
  • Special Master issued a draft Final Report in November of 2017 and the States had an opportunity to provide comment.
  • Special Master filed his Final Report, which included a proposed Judgment and Decree, with the Supreme Court on January 10, 2018.
  • The States agreed to not take exceptions.


  • Montana is entitled to $20,340, plus interest. This amount reflects the cost of replacement water that Montana or its users could have purchased in 2004 and 2006.
  • Montana is not entitled to disgorgement damages. Wyoming’s breach was not knowing, willful or reckless.
  • Montana is not entitled to injunctive relief. There is no cognizable danger of recurrent violation by Wyoming.
  • Montana entitled to costs in the amount of $67,270.87.
  • Montana is only entitled to the costs it incurred through February 10, 2010, the date the Special Master filed his First Interim Report. For the most part, Montana did not prevail on its claims after that date.
  • The Judgment dismisses with prejudice all of the remaining claims in Montana’s Bill of Complaint.


  • The Compact protects pre-1950 water rights in Montana from uses made under post-1950 water rights in Wyoming. If Montana’s pre-1950 water rights are not being satisfied, it must place a call on Wyoming.
  • Montana cannot make a call to fill Tongue River Reservoir unless substantial evidence exists that it will not fill by the end of the water year.
  • Montana must attempt to remedy any water shortages to its pre-1950 water rights through intrastate means before it can place a call on Wyoming.
  • Montana must lift a call when its pre-1950 water rights are satisfied, or it has substantial evidence that Tongue River Reservoir will fill.
  • If Montana makes a valid call, Wyoming must regulate its post-1950 water rights if they have not been regulated already for the benefit of senior water rights in Wyoming.
  • Wyoming can release water stored after the call under post-1950 rights when possible upon request.
  • The Compact does not guarantee Montana a fixed quantity or flow of water, nor does it limit Wyoming to the net volume of water actually consumed in Wyoming prior to January 1, 1950.
  • All pre-1950 water rights in Wyoming can be fully satisfied before Montana is entitled to any water. Essentially, all of Wyoming’s pre-1950 water rights are senior to all of Montana’s water rights, no matter their priority date.
  • Pre-1950 water users in Wyoming can increase their irrigation efficiencies, such as switching to sprinkler irrigation, even if it increases water consumption and interferes with uses in Montana.
  • Wyoming users also maintain the ability to change their water rights under Wyoming law.
  • Any water stored in Wyoming under post-1950 water rights prior a call can be used at any time, including when Montana pre-1950 water rights are not being satisfied.
  • Wyoming reservoirs can continue to operate consistently with Wyoming’s reservoir laws and rules.
  • Montana has a right to fill the pre-Compact capacity of Tongue River Reservoir, or 72,500 acre-feet.
  • Montana must avoid wasting water in its operation of Tongue River Reservoir, and employ good engineering practices.
  • The Decree sets reasonable range for winter outflows from the Tongue River Reservoir at 75 to 175 cubic feet per second.
  • For 2004 and 2006, maximum wintertime carryover of 45,000 AF.
  • Each state must share with the other a list of its surface water rights in the Tongue River Basin. Further, each state must share other information as requested and necessary to administer calls under the Compact, primarily designed to avoid future controversies.
  • The Yellowstone River Compact Commission is still free to modify or supplement the information sharing provisions of the Decree.