The updated 2026 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa, continues to be below average. April runoff in the Missouri River Basin above Sioux City was 1.5 million acre-feet, 51% of average.

“Runoff into the reservoir system was below average for the month of April due to lack of plains snowpack and precipitation,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “Dry conditions are present in 74% of the basin, and drought conditions are expected to persist through July with some expansion likely in Montana and South Dakota. As a result, the runoff forecast was lowered by 0.7 MAF from last month.” 

The 2026 calendar year runoff forecast above Sioux City is 17.1 MAF, 67% of average. The runoff forecast is based on current soil moisture conditions, mountain snowpack, and long-term precipitation and temperature outlooks.

The volume of water stored in the Missouri River Mainstem Reservoir System is currently 49.2 MAF, 6.9 MAF below the top of the carryover multiple use zone.

Fort Peck releases will be increased from 5,000 cubic feet per second to 7,000 cfs in mid-May and are forecast to increase to 8,000 cfs in July. Garrison releases will be increased from 14,000 cfs to 18,000 cfs around mid-May and are forecast to be held at that rate through the summer.

Basin and river conditions continue to be monitored, including plains and mountain snow accumulation, and System regulation will be adjusted based on the most up-to-date information.

Navigation:
Gavins Point Dam releases will continue to provide navigation flow support at 5,500 cfs below full service for the first half of the navigation season. Flow support began April 1 at the mouth of the river near St. Louis, Missouri. The service level was based on the total volume of water stored within the System on March 15, in accordance with the guidelines in the Master Manual. Flow support for the second half of the navigation season, as well as navigation season length, will be based on the storage in the System on July 1.

Mountain Snowpack:
The mountain snowpack was below normal and peaked approximately a month earlier than normal. The Fort Peck reach peaked at 77% of average on March 16 and 74 percent of the 2026 peak remained on May 4. The Garrison reach peaked at 79 percent of average on March 16 and 74% of the 2026 peak remains. Mountain snow normally peaks near April 17. The mountain snowpack graphics can be viewed at: https://go.mil/mr-mtn-snowpack.  

Monthly Water Management Conference Calls for 2026:
The May 2026, monthly conference call will be held Thursday, May 7, 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.

Reservoir Forecasts:

• Gavins Point Dam
  • Average releases past month – 23,800 cfs
  • Current release rate – 23,500 cfs
  • Forecast release rate – 25,100 cfs
  • End-of-April reservoir level – 1206.5 feet
  • Forecast end-of-May reservoir level – 1206.0 feet
  • Notes: The Gavins Point release will be adjusted as needed to provide navigation flow support on the lower Missouri River.
• Fort Randall Dam
  • Average releases past month – 21,900 cfs
  • End-of-April reservoir level – 1355.1
  • Forecast end-of-May reservoir level – 1355.0 feet
  • Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point and to back up the Gavins Point release increases.
• Big Bend Dam
  • Average releases past month – 23,100 cfs
  • Forecast average release rate – 21,200 cfs
  • Forecast reservoir level – 1421.0 feet
• Oahe Dam
  • Average releases past month – 23,200 cfs
  • Forecast average release rate – 21,400 cfs
  • End-of-April reservoir level – 1600.1 feet (down 1.3 feet since March 31)
  • Forecast end-of-May reservoir level – 1599.5 feet
• Garrison Dam
  • Average releases past month – 14,200 cfs
  • Current release rate – 14,000 cfs
  • Forecast release rate – 18,000 cfs
  • End-of-April reservoir level – 1827.1 feet (down 0.2 feet since March 31)
  • Forecast end-of-May reservoir level – 1827.4 feet
  • Notes: Releases will be increased to 18,000 cfs in mid-May
• Fort Peck Dam
  • Average releases past month – 4,800 cfs
  • Current release rate – 5,000 cfs
  • Forecast release rate – 7,000 cfs
  • End-of-April reservoir level – 2222.9 feet (up 0.6 feet since March 31)
  • Forecast end-of-May reservoir level – 2223.7 feet
  • Notes: Releases will be increased to 7,000 cfs in mid-May.

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 648 million kWh of electricity in April. Typical energy generation in April is 696 million kWh. Forecast generation for 2026 is 7.3 billion kWh 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.