Fort Peck Reservoir runoff forecast dries up dry March

Musselshell Missouri confluence

An aerial view shows the confluence of the Missouri and Musselshell Rivers, the UL Bend wilderness and the Crooked Creek fishing access.

A dryer than normal March has resulted in lower inflows to Fort Peck Reservoir this spring.

The lake’s current elevation is 2,233 feet, about 2 feet lower than at the same time last year, and 5 feet lower than the wet spring of 2019. By the end of the month, the U.S. Army Corps of Engineers is predicting the reservoir will rise by only a half-foot.

Crooked Creek Marina’s owners, on the west side of the reservoir, said they wouldn’t recommend launching boats right now because the water is so low, according to this week’s fishing report.

With lower streamflows, the Corps of Engineers updated its runoff forecast in the upper Missouri River Basin to 21.3 million acre-feet, 83% of average.

“Abundant precipitation fell during March in the lower Basin below Sioux City, Iowa; however, March precipitation was less than 50% of normal over much of the upper Basin,” said John Remus, chief of the U.S. Army Corps of Engineers’, Missouri River Basin Water Management Division. “Due to the lack of plains snowpack in 2021, below-average mountain snowpack, and dry upper Basin conditions, we expect upper Basin runoff to be below average.”

The April 1 mountain snowpack in the Fort Peck reach was 88% of average and the snowpack in the Fort Peck to Garrison reach was 94% of average, according to the Corps. By April 1, about 97% of the mountain snow has typically accumulated, peaking near April 15.

Likewise, Canyon Ferry Reservoir is 76% full with inflows close to normal. Below the series of dams near Helena, however, flows in the Missouri River at Cascade were 4,250 cubic feet per second compared to the long-term average of 5,800 cfs.

Bighorn Reservoir on the Montana-Wyoming border is 80% full. The boat ramp at Horseshoe Bend should be usable, as the water level is 3 feet above the minimum for launching. Downstream from the dam, the Bighorn River is flowing at 2,240 cfs. Montana Fish, Wildlife & Parks biologists would prefer to see the river’s level between 2,500 and 3,500 cfs to benefit the trout population.

Montana saw a drier than usual March that has agriculture and wildland fire officials worried.