Montana v. Wyoming
Headline: Court orders Wyoming to pay Montana damages for reducing Tongue River flows and issues a detailed decree governing when Montana can call for water and how reservoirs must be managed, affecting water users in both states.
Holding: The Court awards Montana damages for Wyoming’s reductions in Tongue River flow, directs payment for reservoir improvements, and issues a detailed decree defining Article V(A) protections, calls, and reservoir rules.
- Wyoming must pay damages and costs to Montana for Tongue River flow reductions.
- Montana may place calls to require Wyoming to limit post-1950 storage during shortages.
- Reservoir operations must avoid wasteful outflows and follow set winter flow ranges.
Summary
Background
Montana sued Wyoming over reductions in water flowing at the Tongue River stateline, alleging Wyoming cut available water by 1,300 acre-feet in 2004 and 56 acre-feet in 2006. The Court awarded Montana $20,340 in damages plus 7% interest from the years of the violations, and costs of $67,270.87, to be used for Tongue River Reservoir improvements. The Court received the Special Master’s report and entered a final judgment and decree interpreting the Yellowstone River Compact.
Reasoning
The central question was how the Compact’s Article V(A) protects Montana’s pre-1950 water rights and what steps each State must take to honor those rights. The Court held that Article V(A) protects beneficial pre-1950 appropriative rights but does not guarantee a fixed flow. Montana must place a “call” to trigger protection, and Wyoming must, to the degree physically possible, prevent post-1950 diversions or storage that interfere with those pre-1950 rights. The decree sets rules on storage, reservoir accounting, winter outflow ranges, information exchanges, and when conserved water may be used.
Real world impact
The decree affects how both states operate reservoirs and how water users prioritize deliveries when supplies are tight: post-1950 storage may be held back during a Montana call; Montana’s protected Tongue River storage is defined (generally 72,500 acre-feet, with conditions); and both states must share rights and pumping information. The Court retained jurisdiction for future adjustments. The decree does not address tribal water rights.
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