South Prairie Lake is a highly nutrient-loaded hypereutrophic lake in Black Hawk County, Iowa. Water quality is graded F based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Compared to the 6 other monitored lakes in Black Hawk County, South Prairie Lake ranks #6 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-10-23. Grade methodology: LakeGrade methodology.
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Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 1.6 ft of visibility. Chlorophyll-a: 66.9 µg/L. Trophic State Index: 71.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 66.9 µg/L | F |
| Trophic State Index (TSI) | 71 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near South Prairie Lake
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Fishing South Prairie Lake
Water Quality Trend: ↓ Declining
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.008 m/yr | 5 |
| Chlorophyll-a | ↓ Declining | +3.61 µg/L/yr | 5 |
Water Temperature
South Prairie Lake averages about 77°F at the surface in summer, usually warmest in Jul (about 81°F) and coldest in Sep (about 71°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 29 field readings (2010–2023) via the EPA Water Quality Portal. See the full South Prairie Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of South Prairie Lake, reaching a maximum surveyed depth of 18 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #6 of 7 lakes in Black Hawk County
Cleaner Lakes Within 30 Miles
South Prairie Lake holds Grade F. 3 nearby lakes hold higher grades.
- DMitchell LakeBlack Hawk County · 7.4 mi · Higher grade (F → D)
- DGreen Belt LakeBlack Hawk County · 3.6 mi · Higher grade (F → D)
- DFisher LakeBlack Hawk County · 4.7 mi · Higher grade (F → D)
Nearby Lakes in Black Hawk County
Explore South Prairie Lake across LakeGrade
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Hypereutrophic Lakes in Iowa
More records, surveys & data sources
Reservoir Info (USACE NID)
South Prairie Lake is a man-made reservoir impounded by the Viking Road Detention Dam (completed 1994), built primarily for flood risk reduction on the DRY CREEK; earth-type dam, 22 ft tall and 1,000 ft long.
- Normal storage
- 0 ac-ft
- Max storage
- 1,000 ac-ft
- Drainage area
- 6 sq mi
- Hazard class
- High
- Owner
- City of Cedar Falls
All listed purposes: Flood Risk Reduction;Other.
Source: USACE National Inventory of Dams, NID ID IA03104 · Operator website · Matched by proximity (0.7 km)
Regulated Pollution Sources Nearby
8 EPA-permitted facilities operate within about 5 miles of South Prairie Lake under Clean Water Act (NPDES) discharge permits. 6 facilities have a reported Clean Water Act violation in the past three years.
- Quad State Gauging & MeasurementCedar Falls · 0.4 mi away · NPDES IA0074071Recent violation
- Viking Pump, Inc. - Viking Road FacilityCedar Falls · 0.6 mi away · NPDES IA0078140Recent violation
- University Of Northern IowaCedar Falls · 2.4 mi away · NPDES IA0063941Recent violation
- Cedar Falls Mobile Home VillageCedar Falls · 2.9 mi away · NPDES IA0064033Recent violation
- Hudson City Of StpHudson · 4 mi away · NPDES IA0027243Recent violation
- Cedar Glen Mhc LlcCedar Falls · 4.5 mi away · NPDES IA0061689Recent violation
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
Data Sources
Water quality data from the EPA Water Quality Portal
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2024-10-23
Monitoring stations: 1