Floyd River at Alton, IA
River level and flood forecast · Sioux County
Normal5.8 ftas of Mon 3 PM
The river is 6.2 ft below flood stage (12 ft).
Flow: 63 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 | 22 ft |
| Moderate flood stage | 16 ft |
| Flood stage | 12 ft |
| Action stage | 10 ft |
| Record crest (June 22, 2024) | 26.81 ft |
What floods at each level
From the National Weather Service, highest first.
- 26 ftHwy 10 is flooded and substantial flooding is ongoing near the river throughout Alton.
- 24 ftSeveral houses on the north side of Alton flood. Water approaches Hwy 10 on the north side of Alton. The railroad tracks are also flooded.
- 22 ftMore substantial street flooding begins in Alton including 3rd Ave south of the bridge. Additional structures are also in danger of flooding.
- 20 ftThe lower levees in Alton may begin to be overtopped flooding some nearby industrial businesses. Hwy 60 south of Alton is flooded. Portions of Division St in Alton may also begin to flood and the bridge on 3rd Ave may also be closed.
- 18 ftThe entire flood plain is under water and the river is about 1/2 mile wide. The flooding still primarily only affects agricultural land and county roads.
- 16 ftSignificant amounts of crop and pasture land are flooded.
- 15 ft410th Street and Larch Avenue is inundated. Also 440th Street and Kingbird Avenue is flooded, and the water reaches the bottom of the bridge at CR L14 and 440th Street.
- 12 ftFlooding begins to affect the lower lying agricultural lands along the river.
Highest crests on record
- 26.81 ft — June 22, 2024
- 21.96 ft — September 20, 2018
- 20.87 ft — March 14, 2019
- 20.5 ft — June 21, 2018
- 19.19 ft — May 27, 2013
Recent crests: 13.43 ft (July 31, 2025) · 26.81 ft (June 22, 2024) · 9.09 ft (May 13, 2023) · 6.43 ft (June 25, 2022) · 6.16 ft (July 14, 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 (ALTI4); flow from the U.S. Geological Survey. Readings are provisional. In a flood, follow your local officials and the NWS at weather.gov.