Montana v. Wyoming
Headline: Court orders Wyoming to pay Montana damages for reducing Tongue River flows and issues a decree clarifying when calls, storage, and reservoir rules apply under the Yellowstone River Compact.
Holding: The Court finds Wyoming violated the Yellowstone River Compact, awards Montana $20,340 plus 7% interest and $67,270.87 costs, and enters a detailed decree governing calls, storage, and reservoir operation.
- Requires Wyoming to pay Montana damages, interest, and costs within 90 days.
- Blocks Wyoming from storing water under post-1950 rights during an active Montana call.
- Requires annual sharing of water-rights and groundwater pumping information between states.
Summary
Background
The dispute is between the State of Montana and the State of Wyoming over water from the Tongue River at the Montana–Wyoming stateline. Montana proved Wyoming reduced the river’s available volume by 1,300 acre‑feet in 2004 and 56 acre‑feet in 2006. Montana sought relief under the Yellowstone River Compact, and the Court entered judgment for Montana with money awards and a binding decree about how the Compact must be applied.
Reasoning
The core question was when Wyoming’s diversions or storage violate Montana’s pre‑1950 water rights protected by Article V(A) of the Compact. The Court held Wyoming violated the Compact for the two years identified, awarded Montana $20,340 plus 7% interest from the year of each violation and $67,270.87 in costs, and set rules about how Montana can call for water, how Wyoming must respond, and when Wyoming may store water. The decree explains that Montana must place a clear call (a request for water) to trigger protection, that calls are effective when received, and that Wyoming may be liable even when it was initially physically unable to prevent harmful storage.
Real world impact
The decree protects certain pre‑1950 rights, limits Wyoming’s ability to store water during an active Montana call, defines how much Montana may store in the Tongue River Reservoir each water year (72,500 acre‑feet, with specific carryover rules), and sets a reasonable winter outflow range (75–175 cubic feet per second). The Court also requires routine exchange of water‑rights and groundwater data and allows Montana to use the awarded funds for Tongue River Reservoir improvements. The Court retained jurisdiction for future enforcement.
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