In-stream water rights discussion
Wyoming Water Development Office program manager, Chace Tavelli gives a presentation at a public scoping meeting in Pinedale in mid-April.
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Upper Green River Basin in-stream flow studies begin
by Joy Ufford
April 17, 2026
Wyoming Game and Fish and state water agencies kicked off the process to study and request unallocated Upper Green River Basin (UGRB) in-stream water rights to benefit Colorado cutthroat trouts’ life cycles and state fisheries.
Wyoming Water Development Office (WWDO) and Game and Fish staff presented the Level 1 project at an April public scoping meeting in Pinedale to study in-stream flows and unallocated water rights from six identified stream segments throughout the basin.
"In-stream flow is a three-legged stool with Game and Fish and the State Engineer’s Office," said WWDO program manager Chace Tavelli.
Last year, Game and Fish designated "critical" segments of six creeks – all on public lands – and asked WWDO to determine if these particular unallocated waters have sufficient naturally flowing cubic-flow-per-second (cfs) needed to improve Colorado cutthroat trout habitats during its life cycle.
Wyoming Game and Fish requests specific in-stream flows in its biological reports to benefit its fisheries.
The WWDO contracted consultant Mike Fuller, of Hydrologic Solutions, LLC to design the studies of the six Upper Green stream segments identified by Game and Fish. Fuller described the six segments – West Horse Creek (3.55 miles), Klondike Creek (2.75 miles), Rock Creek (6.39 miles), South Beaver Creek (5.98 miles), North Horse Creek (16.44 miles) South Horse Creek (12.77 miles) and Maki Creek (3.55 miles).
"We have not found any water rights at these segments or above them," Fuller said. "We did fairly thorough evaluations."
The project will measure "unassigned" in-stream flows upstream from any existing water diversions and water rights’ holders and look at extensive historic gauge, depth and velocity data. "We’re not here to debate in-stream flows," Tavelli said. "We have a statutory duty to do these studies. ... The water does stay in the stream."
Game and Fish In-Stream Biologist Sydney McAndrews said the unallocated water could be essential for the Colorado cutthroat and fisheries. To select segments, they moved past a private boundary or existing water right "and then go upstream as far as reasonable in the watershed." Fuller will measure each segment’s depth and velocity at its downstream end, compile historic and current data, past studies and reports, then make field visits in May and compile a complete hydrologic analysis "to re-create streamflow within these creeks," he said.
Fuller is also required to perform a "storage analysis" to meet or adjust the in-stream flow rates for the year per Game and Fish. "We will look at what types of storage would be required to meet the water-rights requirements."
Tavelli emphasized that permitting new water rights does not add or take away allocated water to the tributaries or the Upper Green itself.
He said irrigation and water-rights holders would not be affected; none of the in-stream flow being quantified is allocated, he repeated.
"It does not impact previously existing water rights. The water stays in the river; it doesn’t get pulled out. ... It’s not a sum total. Only within this segment is the amount of water being requested for permitting."
In the case of this year’s dry winter and spring likely lowering Upper Green water flows, McAndrews said in low snow years, the flows might not be met. "Our requests for flows are only if naturally available for what we request."
"If Game and Fish requests 10 cfs and there’s only 4 cfs in the creek – that’s hydrology," Tavelli said.
When Fuller completes the Upper Green River Basin Level 1 hydrology analysis, Tavelli and others will review the report. The final report is sent to the SEO for close scrutiny. The State Engineer’s Office will then hold a public meeting next year, probably in Pinedale, take comments, and determine the status of Wyoming Game and Fish’s water-rights application.
For detailed maps and specifics on the six designated creek segments for the Upper Green River Basin Level 1 Study, go to the Wyoming Water Development Commission website, https://wwdc.state.wy.us/, under "In-Stream Flows."
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