- Bighorn River Basin runoff forecast is well below average.
- North Platte Basin runoff projected at just 50 percent of normal.
- Key reservoirs remain below full capacity but functional.
- Irrigation supply expected to be near normal despite shortfall.
- Hydropower production could be affected by lower inflows.
Monday, June 16, 2025 — The U.S. Bureau of Reclamation’s Dry outlook for Bighorn and North Platte River systems raises water supply concerns for Wyoming.
Bighorn River Basin: Low Runoff Expected into Key Reservoirs.
Reclamation released its June water forecast
on Wednesday, showing significantly below-average snowmelt runoff for the Bighorn River Basin in north-central Wyoming. The runoff projections are based on expected inflows from June through July into four major reservoirs.
Bighorn Lake, fed by the Bighorn River, is projected to receive approximately 370,000 acre-feet of water, which is just 47 percent of the 30-year average of 782,000 acre-feet. As of June 1, Bighorn Lake was at 88 percent of its conservation capacity.
Buffalo Bill Reservoir, which stores runoff from the Shoshone River, is forecast to take in 320,000 acre-feet, which is 61 percent of its historical average. On June 1, it was 74 percent full.
The inflow into Boysen Reservoir from the Wind River is expected to be approximately 240,000 acre-feet, which represents only 45 percent of the long-term average. Boysen stood at 75 percent capacity at the start of June.
Bull Lake Reservoir, which captures runoff from Bull Lake Creek, is expected to receive 94,000 acre-feet of snowmelt—82 percent of the 30-year average. As of June 1, the reservoir was just 45 percent full.
These reservoirs, combined, have a total capacity of 2.6 million acre-feet and play a crucial role in irrigation and hydropower for the region. Power is generated at facilities tied to Boysen and Buffalo Bill Reservoirs in Wyoming and Yellowtail Powerplant in Montana.
North Platte River Basin: Runoff Half of Normal.
Reclamation’s June forecast also reported troubling numbers for the North Platte River Basin. Total snowmelt runoff from April through July is expected to reach 476,000 acre-feet, only 50 percent of the 30-year average. Nearly 244,000 acre-feet had already entered the system by the end of May.
As of May 31, the North Platte Reservoir System held about 1.64 million acre-feet of water, which is roughly 81 percent of the average for this time of year. The system can hold up to 2.82 million acre-feet at conservation capacity.
Despite low natural flows, an irrigation allocation was declared on May 14. Reclamation noted that “a near normal irrigation supply is anticipated for the year.”
Reservoir Releases Adjusted.
Water releases from the system’s reservoirs are being adjusted to balance storage and supply:
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Seminoe Reservoir is currently releasing 2,000 cubic feet per second through the Miracle Mile section of the river.
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Gray Reef Reservoir is releasing 1,200 cubic feet per second, with flows expected to peak near 3,300 cubic feet per second.
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Guernsey Reservoir has paused releases for now but will vary from 0 to 5,000 cubic feet per second through September to meet irrigation needs.
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Pathfinder Reservoir is not expected to spill this spring based on current conditions.
The North Platte system includes seven reservoirs, from Seminoe upstream to Guernsey downstream. In addition to agricultural use, the system supports six hydropower plants that provide electricity to tens of thousands of homes.
The below-average snowpack and runoff in both basins signal a challenging summer ahead for water managers, farmers, and hydropower operators. While irrigation deliveries may remain steady for now, storage levels and natural inflows will be closely watched through the season.
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