Below-average runoff leads to reduced navigation flow support and shortened season

June runoff in the Missouri River Basin above Sioux City, Iowa was 2.9 million acre-feet, 52% of average. The updated 2026 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa, continues to be below average.

“Mountain snowpack peaked much earlier than normal this year and completely melted by the end of June,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “June runoff was below-normal to well-below-normal in every reach due to below average precipitation, dry basin conditions and below average mountain snowpack. Dry conditions are expected to continue in July.” The 2026 calendar year runoff forecast above Sioux City is 15.5 MAF, 60% of average, and the same as last month’s forecast. The runoff forecast is based on current soil moisture conditions, mountain snowpack, and long-term precipitation and temperature outlooks.

System storage on July 1 was 49.1 MAF, 7.0 MAF below the top of the carryover multiple use zone. “Based on the July 1 System storage, flow support for navigation decreased from 5,500 cfs below full-service to minimum service,” said Remus. “Per the guidelines in the Master Manual, this will also result in a shortened navigation flow support season ending Nov. 15 at the mouth of the Missouri River. A full navigation support season typically ends Dec. 1. Gavins Point releases were reduced to 24,000 cfs in early July due to recent rainfall and to account for the decrease in navigation flow support.”

“The monthly study indicates that the winter release from Gavins Point, which is based on the Sept. 1 System storage check, will likely be at the minimum rate of 12,000 cfs,” added Remus. Basin and river conditions continue to be monitored, including soil moisture and drought conditions, and System regulation will be adjusted based on the most up-to-date information.

Navigation: Gavins Point Dam releases will be set to provide navigation flow support at minimum service at the four target locations (Sioux City, Omaha, Nebraska City, and Kansas City). The flow support season length will be shortened, ending November 15 at the mouth of the Missouri River.

Mountain Snowpack: The mountain snowpack melted quickly due to warmer-than-normal temperatures during the spring and early summer. By June 25, all the snow had melted in both the reach above Fort Peck and the Fort Peck to Garrison reach. The mountain snowpack peaked in the Fort Peck reach on March 16 at 77% of average, while the Garrison reach peaked on March 16 at 79% of average. Mountain snowpack normally peaks near April 17 and melts out in both reaches around July 1. The mountain snowpack graphics can be viewed at: https://go.mil/mr-mtn-snowpack.

Monthly Water Management Conference Calls for 2025: The July 2026 monthly conference call will be held Thursday, July 9, to inform basin stakeholders of current weather and runoff forecasts and the planned operation of the reservoir system in the coming months. Presentation materials will be available via webinar. The call is intended for Congressional delegations; Tribes; state, county and local government officials; and the media. It will be recorded in its entirety and made available to the public on our website at https://go.mil/mr-news. Slides accompanying the call will be available at: https://go.mil/mr-monthly-slides.

Reservoir Forecasts

Gavins Point Dam

• Average releases past month – 25,000 cfs
• Current release rate – 24,000 cfs
• Forecast release rate – 24,700 cfs
• End-of-June reservoir level – 1206.6 feet
• Forecast end-of-July reservoir level – 1206.0 feet
• Notes: The Gavins Point release will be adjusted to provide navigation flow support on the lower Missouri River.

Fort Randall Dam

• Average releases past month – 23,100 cfs
• End-of-June reservoir level – 1355.0 feet
• Forecast end-of-July reservoir level – 1355.3 feet
• Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point and to back up Gavins Point releases.

Big Bend Dam

• Average releases past month – 22,600 cfs
• Forecast average release rate – 24,400 cfs
• Forecast reservoir level – 1420.4 fee

Oahe Dam

• Average releases past month – 21,900 cfs
• Forecast average release rate – 23,900 cfs
• End-of-June reservoir level – 1597.9 feet (down 0.6 feet from May 31)
• Forecast end-of-July reservoir level – 1596.5 feet

Garrison Dam

• Average releases past month – 17,800 cfs
• Current release rate – 18,000 cfs
• Forecast release rate – 18,000 cfs
• End-of-June reservoir level – 1828.2 feet (up 1.6 feet from May 31)
• Forecast end-of-July reservoir level – 1828.6 feet
• Notes – Releases will be maintained at 18,000 cfs through mid-September.

Fort Peck Dam

• Average releases past month – 6,800 cfs
• Current release rate – 7,000 cfs
• Forecast average release rate – 7,000 cfs
• End-of-June reservoir level – 2223.9 feet (up 0.7 feet from May 31)
• Forecast end-of-July reservoir level – 2223.6 feet
• Notes: Releases will be maintained at 7,000 cfs through September.

The forecast reservoir releases and elevations discussed above are not definitive. Additional precipitation, lack of precipitation or other circumstances could cause adjustments to the reservoir release rates.

Hydropower: The six mainstem power plants generated 696 million kWh of electricity in June. Typical energy generation for June is 841 million kWh. The power plants are expected to generate 7.2 billion kWh this year, compared to the long-term average of 9.3 billion kWh. To view the detailed three-week release forecast for the mainstem dams, go to https://go.mil/mr-3wk-fcast.

The Missouri Basin Web App provides links to these reports and others that are updated more frequently. https://go.mil/mr-webapp.