Upper Big Sioux HUC8 10170201
A 4,230 km² sub-basin of the Missouri region in SD. Drought coverage is from the US Drought Monitor (map of 2026-10-13); streamflow classes place each USGS gauge's latest reading against its own day-of-year record.
Health score
70
Moderate
Drought index
174
Moderate
Area in D2+
0%
0% exceptional (D4)
Gauges below normal
0%
of 4 reporting
Median flow
86%
p46 of record
Water assets
4,205
4 springs · 3,369 wells
USGS gauges (5)
- BIG SIOUX RIVER NEAR FLORENCE, SD064792150 cfsp28 · normal
- BIG SIOUX RIVER AT WATERTOWN, SD064795002 cfsp43 · normal
- BIG SIOUX RIVER NEAR WATERTOWN, SD064794384 cfsp48 · normal
- BIG SIOUX RIVER NEAR CASTLEWOOD, SD0647952527 cfsp52 · normal
- BIG SIOUX RIVER BELOW WATERTOWN, SD0647952021 cfsno long-term record
Recent conditions
| Date | DSCI | D2+ % | Gauges low | Flow pct |
|---|---|---|---|---|
| 2026-10-21 | 174 | 0 | 0/4 | p46 |
| 2026-10-20 | 174 | 0 | 0/4 | p49 |
| 2026-10-19 | 174 | 0 | 0/4 | p48 |
| 2026-10-18 | 174 | 0 | 0/4 | p44 |
| 2026-10-17 | 174 | 0 | 0/4 | p45 |
| 2026-10-16 | 174 | 0 | 0/4 | p41 |
| 2026-10-15 | 174 | 0 | 0/4 | p43 |
| 2026-10-14 | 174 | 0 | 0/4 | p49 |
| 2026-10-13 | 174 | 0 | 0/4 | p50 |
| 2026-10-12 | 174 | 0 | 0/4 | p49 |
| 2026-10-11 | 174 | 0 | 0/4 | p50 |
| 2026-10-10 | 174 | 0 | 0/4 | p49 |
| 2026-10-09 | 174 | 0 | 0/4 | p49 |
| 2026-10-08 | 174 | 0 | 0/4 | p37 |
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