Sioux Falls
South Dakota

Stream Water Quality

Once a week, in every season, the city takes a bottle and a meter to five places on the water: four along the Big Sioux River as it crosses the city, and one on Skunk Creek where it passes Marion Road. This is 4,468 of those visits, from June 5, 2012 to October 8, 2026, one series per place, listed the way the river runs — upstream first.

Where South Dakota publishes a threshold for a place and a parameter, it is drawn on the chart and the rule is cited beneath it. Nothing here is scored against it. A dashed line is a number the state wrote down, not a verdict on the day's sample.

  1. Big Sioux River I-90

    Last sampled October 8, 2026 · 884 samples

    E. coli
    770 per 100 mL Aug 27, 2026
    Dissolved oxygen
    8.64 mg/L Oct 8, 2026
    Temperature
    15 °C Oct 8, 2026
    Nitrate
    0.01 mg/L Aug 27, 2026
    E. coli, last twelve months · 16 samples

    Immersion recreation not supported for E. coli and the fishery not supported for suspended solids; both carry approved TMDLs (Category 4A). Domestic water supply fully supported.

  2. Big Sioux River Falls Park

    Last sampled October 8, 2026 · 800 samples

    E. coli
    114 per 100 mL Aug 27, 2026
    Dissolved oxygen
    10.63 mg/L Oct 8, 2026
    Temperature
    15.8 °C Oct 8, 2026
    Nitrate
    0.02 mg/L Aug 27, 2026
    E. coli, last twelve months · 16 samples

    Immersion and limited-contact recreation not supported for E. coli, the fishery not supported for suspended solids; both carry approved TMDLs (Category 4A). Domestic water supply not supported for total dissolved solids — 303(d)-listed, TMDL scheduled 2035.

  3. Big Sioux River Bahnson

    Last sampled October 8, 2026 · 925 samples

    E. coli
    365 per 100 mL Aug 27, 2026
    Dissolved oxygen
    13.07 mg/L Oct 8, 2026
    Temperature
    15.9 °C Oct 8, 2026
    Nitrate
    0.81 mg/L Aug 27, 2026
    E. coli, last twelve months · 16 samples

    Immersion and limited-contact recreation not supported for E. coli; TMDL approved (Category 4A). Fishery fully supported.

  4. Big Sioux River Timberline

    Last sampled October 8, 2026 · 954 samples

    E. coli
    461 per 100 mL Aug 27, 2026
    Dissolved oxygen
    11.65 mg/L Oct 8, 2026
    Temperature
    16 °C Oct 8, 2026
    Nitrate
    2.3 mg/L Aug 27, 2026
    E. coli, last twelve months · 16 samples

    Immersion and limited-contact recreation not supported for E. coli and the fishery not supported for suspended solids; both carry approved TMDLs (Category 4A).

  5. Skunk Creek Marion Road

    Last sampled October 8, 2026 · 905 samples

    E. coli
    517 per 100 mL Aug 27, 2026
    Dissolved oxygen
    9.22 mg/L Oct 8, 2026
    Temperature
    15 °C Oct 8, 2026
    Nitrate
    0.18 mg/L Aug 27, 2026
    E. coli, last twelve months · 16 samples

    Limited-contact recreation not supported for E. coli — 303(d)-listed (Category 5); the state issued an E. coli TMDL in 2025. Fishery fully supported.

Read one parameter across the river

The same numbers, turned the other way: one parameter at a time, all four Big Sioux sites on one chart from upstream to downstream, with Skunk Creek beneath.

From the city's SWQ Samples table and SWQ Locations layer, as of October 12, 2026. 964 sampling dates; 269 samples measured nothing at all and are kept in the record; 44 published values fall outside what the instrument could have read and are listed but not charted; 7 rows published twice for one site and instant are read as one; 3 rows whose meter read 0 in every field are read as unmeasured on those fields. Site names and positions come from the Locations layer. Thresholds are quoted from ARSD 74:51:01 and the status lines from the 2024 Integrated Report .