Milner Dam near Burley, Idaho.

U.S. Bureau of Reclamation Upper Snake River water managers could cease spill operations at Milner Dam by the end of May.

A strong supply of water in the region drove the spill effort.

Outflows from Milner occur in a quarter to a third of water years, said Brian Stevens, water operations supervisor for Reclamation’s Upper Snake region in Heyburn, Idaho.

“Good carryover from last year coupled with good precipitation has driven the (2024) spill past Milner,” he said.

Milner, outside Burley, is the farthest downstream of the Upper Snake dams. All water upstream is allocated to water right holders. All water downstream comes from springs and return flows, such as post-irrigation water.

Reclamation from March 22 to May 13 released an average of 5,700 cubic feet per second each day past Milner, about 600,000 acre-feet overall, Stevens said.

Also since late March, Reclamation released unstorable water past dams at American Falls and Lake Walcott, which “caused the unstorable water to be spilled past Milner,” he said.

Volumes in headwater reservoirs Jackson Lake in Wyoming and Palisades in eastern Idaho, and most of the other Upper Snake reservoirs, also contributed to the need to spill water past Milner, Stevens said.

Jackson at 82% full and Palisades at 68% have met their flood-control space requirements, he said.

“With the decrease in outflow from Palisades combined with the increased irrigation diversions as temperatures warm in the next week or two, Milner spill could end,” Stevens said.

The spill operations made more water available for Eastern Snake Plain Aquifer recharge operations, he said.