Missouri River Basin Water Management

June runoff in the Missouri River Basin above Sioux City, Iowa was 3.3 million acre-feet, 60% of average. The updated 2025 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa, is 19.1 MAF, 74% of average, and slightly lower than last month’s forecast. The runoff forecast is based on current soil moisture conditions, mountain snowpack, and long-term precipitation and temperature outlooks.

The June 2025 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa, continues to be below average. “Heavy rainfall in western and central North Dakota and South Dakota during May supplemented the mountain snowmelt runoff,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division.

The updated 2025 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 1.4 million acre-feet, 48% of average. “Runoff into the reservoir system was below average for the month of April, and runoff was below average in all reaches,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “Drought or abnormally dry conditions are currently present in 75% of the basin, and conditions have worsened in the Fort Peck reach and parts of the Garrison reach in the last month. As a result, the runoff forecast was lowered by 1.9 MAF from last month.”

The 2025 calendar year runoff forecast above Sioux City is 22.1 MAF, 86% of average. The runoff forecast is based on current soil moisture conditions, plains snowpack, mountain snowpack, and long-term precipitation and temperature outlooks. Average is 25.7 MAF. The March 3 mountain snowpack in the Fort Peck reach was 89% of average, while the mountain snowpack in the Fort Peck to Garrison reach was 91% of average. By March 1, about 79% of the total mountain snowfall has typically accumulated. Mountain snow normally peaks near April 17.

The updated 2025 calendar year runoff forecast for the Missouri River Basin above Sioux City, Iowa, continues to be below average. January runoff in the Missouri River Basin above Sioux City was 0.7 million acre-feet, 92% of average. Runoff was near or below average for most of the Missouri River Basin, and most of the upper basin had below-normal precipitation.