E. coli
E. coli · per 100 mL at every place the city samples, upstream to downstream. The Big Sioux sites share one chart because they share one water; Skunk Creek gets its own, because the state assigns it different uses and different numbers.
The Big Sioux, last twelve months
- I-90
- Falls Park
- Bahnson
- Timberline
64 samples · 35 to 2,420 per 100 mL
Immersion recreation — below 235 in any one sample, May 1 to Sept 30 · ARSD 74:51:01:50The Big Sioux, 2012 to 2026
- I-90
- Falls Park
- Bahnson
- Timberline
2,040 samples · 1.05 to 24,196 per 100 mL
Immersion recreation — below 235 in any one sample, May 1 to Sept 30 · ARSD 74:51:01:50Skunk Creek at Marion Road
524 samples · 1 to 24,196 per 100 mL
Limited-contact recreation — below 1,178 in any one sample, May 1 to Sept 30 · ARSD 74:51:01:51Values cluster at 2,420 and 24,196 — the IDEXX Quanti-Tray ceilings. Those samples were at least that high, not exactly that high.
From the city's SWQ Samples table, as of October 12, 2026. 3 published E. coli values fall outside what the instrument could have read; they are listed on the site pages and left off these charts. Dashed lines are published thresholds with the rule cited, drawn for the season the rule names. No sample here is scored against them.