Montana Issues Call on Wyoming Water to Ensure Tongue River Reservoir Fills
HELENA, Mont. – The Montana Department of Natural Resources and Conservation (DNRC) announced today that based on current drought and storage conditions in the Tongue River Basin, Montana will place a call on Wyoming water users effective May 5, 2026, under the Yellowstone River Compact (YRC). The Tongue River originates in the Bighorn Mountains in Wyoming and flows into Tongue River Reservoir (Reservoir) near the Montana state line, with Wyoming snowpack supplying the majority of the river’s annual flow and spring runoff. The call is being made to ensure that the Reservoir can fill before the end of the water year, which is September 30.
The Yellowstone River and its tributaries span Montana, Wyoming, and North Dakota, with most tributary headwaters, including the Tongue, Powder, Clarks Fork of the Yellowstone, and Bighorn rivers, originating in Wyoming and most of the mainstem river located in Montana. The YRC, approved in 1950, apportions the waters of the Yellowstone River and its tributaries among the three states.
Montana is placing this water call under the YRC and following guidance from the 2018 U.S. Supreme Court ruling in Montana v. Wyoming. The call applies to water rights established after January 1, 1950, but does not affect most household or livestock uses. The action is intended to help ensure water for Montana’s senior water right for the Tongue River Reservoir, which dates back to April 21, 1937. Water rights from before 1950 are not subject to this call under the compact.
To ensure coordination, predictability and transparency on the decision of whether to make a call, the DNRC developed a Call Guide (Guide) with input and feedback from the Wyoming State Engineer’s Office. The Guide uses snowpack, precipitation, reservoir storage data and historic outcomes to determine when and how a call should be placed. This approach provides clear, repeatable criteria and ensures both states are working from the same information. The Guide also incorporates input from the Tongue River Water Users Association and other water users in the basin, supporting locally informed decisions and basin-wide transparency.
“We have great working relationships with Wyoming’s State Engineer and water users in the basin, and that trust is critical when we need to act quickly in a dry year,” said Anna Pakenham Stevenson, DNRC Water Resources Division administrator. “Since everyone can see and understand the data and the guide we use to make a call, we consistently receive full support when it’s time to make a call.”
Why is the call being made now? Current water conditions show that snowpack across the Tongue River Basin is the lowest it’s been in the past 43 years. Tongue River Reservoir is also not holding enough stored water to make up for the lack of snowpack in the basin. Together, these conditions point to a limited water supply in a basin that depends heavily on spring precipitation and is vulnerable to drought.
The YRC provides a process for Montana and Wyoming to manage and protect water rights during dry years. Because the Reservoir has senior rights, Montana can request that Wyoming curtail newer (post-1950) water uses to help meet Montana’s water needs under the compact.
“Conditions in the Tongue River Basin this year clearly meet the criteria for a YRC call, and our decision is grounded in science, transparency and longstanding cooperation with Wyoming,” said Pakenham Stevenson. “The call is necessary to ensure Tongue River Reservoir can fill and continue to reliably serve irrigators, and communities through the coming season.”
Under the Guide, snowpack and rainfall are monitored at key locations in Wyoming, and the need for a call is assessed weekly beginning April 1. If snow, rain, or storage remains low, the state must keep the call in place until “Montana reasonably believes based off substantial evidence that the Reservoir will” fill. The most recent YRC call on the Tongue River was made on April 1, 2022, and was lifted on May 9, 2022, after hydrologic conditions improved in the basin.
DNRC will continue to monitor hydrologic and storage conditions in the Tongue River Basin on a daily basis throughout the spring runoff period. If conditions improve such that Montana reasonably believes based off substantial evidence that the Reservoir will fill by the end of the water year, Montana will lift the call on Wyoming. If the Reservoir does not fill by the end of runoff, Montana will call for the release of stored water under post-1950 water rights in Wyoming that was stored after May 5, in an amount equal only to the volume the Reservoir is short of filling.
For more information about the Yellowstone River Compact and DNRC’s administration of the YRC, visit: https://www.usgs.gov/mission-areas/water-resources/science/yellowstone-river-compact-commission.
####
Tags: