Big Sioux River near Jefferson, SD
River level and flood forecast · Union County
Normal9.6 ftas of Mon 2:30 PM
The river is 21.4 ft below flood stage (31 ft).
Flow: 973 cubic feet per second (USGS).
The last 7 days and the forecast
NWS forecast issued Sun, Dec 31, 6 PM. Forecasts change as rain falls and as upstream water arrives.
Flood stages
| Major flood stage | 40 ft |
| Moderate flood stage | 35 ft |
| Flood stage | 31 ft |
| Action stage | 28 ft |
| Record crest (June 24, 2024) | 44.5 ft |
What floods at each level
From the National Weather Service, highest first.
- 42 ftThe lowest portions of Hwy 12 may begin to flood.
- 40.5 ftAt least a couple farmsteads begin to flood.
- 37 ftWater begins to surround some farmsteads near 329th.
- 35 ftThe lowest portions of 329th are flooded and the floodplain on the South Dakota side is over a mile wide in some areas.
- 31 ftSignificant flooding of crop and pasture land begins.
Highest crests on record
- 44.5 ft — June 24, 2024
- 40.42 ft — March 17, 2019
- 38.4 ft — June 26, 2018
- 36.74 ft — September 18, 2019
- 24.55 ft — April 1, 2020
Recent crests: 15.4 ft (July 8, 2025) · 44.5 ft (June 24, 2024) · 22.39 ft (April 15, 2023) · 17.57 ft (June 2, 2022) · 14.48 ft (August 31, 2021)
Up and down the river, and nearby
Not an official source. River levels, forecasts, flood stages and impacts are from the National Weather Service (BSJS2); flow from the U.S. Geological Survey. Readings are provisional. In a flood, follow your local officials and the NWS at weather.gov.