World
A 1900 Water Right, a 181,600 Acre-Foot Gap
Idaho's water director curtailed 6,400 junior aquifer pumpers in May, protecting a senior right dating to October 1900. The settlement that kept most users online was calibrated for a river delivering more than 2026 is.
Mathew Weaver, Idaho's water director, ordered curtailment May 15 for 6,400 junior groundwater pumpers, citing a 181,600 acre-foot projected shortfall in the Eastern Snake Plain Aquifer.
The order protects the Surface Water Coalition, seven irrigation entities led by Twin Falls Canal Company. Twin Falls filed its surface water right in October 1900. Under Idaho's prior appropriation doctrine, any right recorded after October 11 of that year yields first when supply runs short.
About 80 percent of Twin Falls Canal's supply comes from aquifer-fed springs, so upstream pumping directly cuts canal flow. Twin Falls faces a 137,700 acre-foot deficit this season; American Falls Reservoir District No. 2 carries the remaining 43,900. Together the coalition manages more than 500,000 acres of southern Idaho farmland.
The 6,400 pumpers draw from nine groundwater districts organized under the Idaho Ground Water Appropriators. IGWA's executive director is Lara Herway. The nine districts collectively irrigate roughly 920,000 acres of eastern Idaho potatoes, grain, and sugar beets.
IDWR tracks the dispute in acre-feet per season, the standard unit for conjunctive administration in Idaho. No separate daily draw figure appears in the curtailment order.
The 2024 curtailment lasted roughly three weeks before a settlement paused it, triggered by a 74,100 acre-foot shortfall. The 2026 figure is 145 percent larger. That settlement required the nine districts to reduce annual pumping by 240,000 acre-feet and deliver 75,000 acre-feet per year to the senior holders.
The 240,000 acre-foot reduction target exceeds the aquifer's roughly 200,000 acre-foot annual overdraft, suggesting the deal was calibrated for average inflows. A Bureau of Reclamation and Army Corps joint forecast, issued April 2, put Snake River inflow at 70 percent of average through July.
Brian Murdock, continuing his family's 135-year potato legacy in Bingham County, estimated $3 million in personal exposure during the 2024 curtailment. His holding amounts to less than one percent of the junior acreage now at risk.
The arithmetic points to a built-in constraint: the 2024 deal was sized for average Snake River inflows, and 2026 is delivering 70 percent of average.
Weaver issues an updated order in July. If the mitigation pool cannot cover 181,600 acre-feet, 6,400 pumps stop mid-season across 920,000 acres.