Changes Coming For Eastern Idaho Irrigators

Officials with the Idaho Department of Water Resources are giving water users a heads-up in the Big Lost, Little Lost, and Raft River basins.

Those areas, now part of the Eastern Snake Plain Aquifer Area of Common Groundwater Supply, thanks to last year's passage of Senate Bill 1341, will be subject to future water delivery calls by the Surface Water Coalition (SWC).  For parts of the Big Lost and Little Lost basins, those calls won’t take effect until April 1st, 2027.  However, portions of the Big Lost Basin up to Mackay and the Little Lost Basin at Howe will be subject to delivery calls during the upcoming 2026 irrigation season. 

The Raft River Basin will also be phased in starting next year.

Earlier this month, Mathew Weaver, Director of the Idaho Department of Water Resources, found that 1,005 ground water rights within the expanded area of administration were brought into the SWC delivery call proceeding and could have become subject to administration.

However Weaver noted, "The material injury caused by the diversion and use of water under these newly included ground water rights is delayed or long range."  The Director also mentioned that "the economic impact of immediate and complete curtailment would be severe,”

Weaver concluded that “the priority administration of these newly included groundwater rights should be phased-in to provide the affected water users a reasonable time to implement a mitigation plan “to lessen the economic impact of immediate and complete curtailment.”

“Senate Bill 1341 instructs IDWR to investigate the impact of tributary basins on the ESPA and Snake River Reach Gains on which the SWC depends to fulfill their senior water rights,” said Brian Patton, IDWR Deputy Director.  “Our analysis shows that it is appropriate to add the Big Lost, Little Lost and Raft River basins into the Eastern Snake Plain Aquifer Area of Common Groundwater Supply (ESPA ACGWS).  The legislation also directs IDWR to give water users advance notice about these findings.

“Groundwater users within these tributary basins will be subject to the SWC delivery call, so groundwater users are encouraged to establish a mitigation plan or join an existing mitigation plan to shield themselves from possible curtailment in the future from the SWC delivery call,” Patton added.

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