Idaho reports the Eastern Snake Plain Aquifer lost 600,000 acre feet this year
IDWR hydrologists told the Water Resource Board on August 26, 2026 that the ESPA had no change from 2024 to 2025 and then a net reduction of 600,000 acre feet in 2026, measured across 329 monitoring wells. The Upper Snake reservoir system sat at 18 percent.
- ESPA change, 2026
- -600,000 AF
- Monitoring wells
- 329
- Upper Snake system
- 18% of capacity
- Assignment pool, no-fill tiers
- $50.80 to $61.80/AF
What happened
IDWR briefed the Idaho Water Resource Board on August 26, 2026: the Eastern Snake Plain Aquifer had no change in volume from 2024 to 2025, and a net reduction of 600,000 acre feet in 2026, based on 329 monitoring wells measured before the irrigation season, leaving the aquifer roughly 100,000 acre feet below its 2015 level. Spring flows at Thousand Springs and in the Blackfoot to Minidoka reach are expected to decline.
The same day the Water District 1 watermaster reported the Upper Snake reservoir system at 18 percent of capacity, drafting about 21,000 acre feet a day, with carryover on pace to be very low. The system did not fill in either 2025 or 2026. Modeling credits Board recharge, private recharge, and pumping reductions with a combined net storage gain of 2.8 million acre feet, which moderates but does not reverse the decline.
What it means if you own water here
A shrinking aquifer under conjunctive management means more curtailment pressure on junior groundwater users next year, and therefore more demand for the leased storage water that mitigation plans run on. Senior rights and banked water are the scarce inputs.
Because the reservoir system did not fill, the higher Tier 6 and 7 rental rates ($50.80 and $61.80 per acre foot) governed Water District 1 assignment-pool rentals this season. Scarcity moved the posted price automatically.
Article Sources
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- IDWR news release, August 26, 2026. ESPA water volume update and impact of managed recharge.
- Water District 1. Watermaster report, August 26, 2026.
- Water District 1. 2026 Rental Pool Procedures (tier rates).
- Capital Press, August 28, 2026. Eastern Snake Plain Aquifer volume plunges in 2026 (about 100,000 acre feet below 2015).