Big Sioux River near Castlewood, SD

River level and flood forecast · Hamlin County

Normal4.8 ftas of Mon 3:45 PM

The river is 4.2 ft below flood stage (9 ft).

Flow: 26 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	16 ft
Moderate flood stage	11 ft
Flood stage	9 ft
Action stage	8 ft
Record crest (April 7, 1997)	13.19 ft

What floods at each level

From the National Weather Service, highest first.

18 ft479th Avenue begins to flood south of Castlewood.
17 ftHighway 22 begins to flood, as does 181st Street, and water reaches the bottom of the bridge on 459th Avenue south of Castlewood.
16 ftThe river will be about 1 mile wide and many farm buildings around Castlewood will be flooded.
15 ftThe water reaches the bottom of the bridges on Highway 22 and 181st Street.
13 ftMajor agricultural flooding begins south of Castlewood.
11 ftSignificant amounts of pasture and other agricultural lands will be flooded.
10 ft184th Street begins to flood.
9 ftWater overtops the culvert on 184th Street and significant agricultural flooding begins north of Castlewood.
8 ftMinor flooding of low-lying agricultural lands along the river will begin.

Highest crests on record

13.19 ft — April 7, 1997
12.39 ft — March 28, 2019
12.29 ft — March 23, 2011
12.27 ft — April 8, 2001
11.98 ft — March 15, 2010

Recent crests: 11.44 ft (July 29, 2025) · 11.64 ft (April 13, 2023) · 10.7 ft (June 1, 2022) · 8.37 ft (April 10, 2021) · 9.53 ft (April 3, 2020)

Up and down the river, and nearby

See it on the live map →Radar & warnings for Hamlin County NWS gauge page USGS gauge 06479525

Not an official source. River levels, forecasts, flood stages and impacts are from the National Weather Service (CSWS2); flow from the U.S. Geological Survey. Readings are provisional. In a flood, follow your local officials and the NWS at weather.gov.