Thomas Mitchell Lake is a 4-acre productive, nutrient-rich eutrophic lake in Polk County, Iowa. Water quality is graded D based on 2 sampling years through 2024. Water clarity is declining over recent sampling years. Compared to the 11 other monitored lakes in Polk County, Thomas Mitchell Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-09-09. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Very murky, less than 3.3 ft of visibility. Chlorophyll-a: 13.2 µg/L. Trophic State Index: 58.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.3 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 13.2 µg/L | C |
| Trophic State Index (TSI) | 58 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 4 acres |
Where to stay near Thomas Mitchell Lake
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Fishing Thomas Mitchell Lake
Water Quality Trend: → Stable
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.06 m/yr | 2 |
| Chlorophyll-a | ↑ Improving | -11.5 µg/L/yr | 2 |
Location & Depth Map
Free interactive depth-contour map of Thomas Mitchell 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 #3 of 12 lakes in Polk County
Cleaner Lakes Within 30 Miles
Thomas Mitchell Lake holds Grade D. 2 nearby lakes hold higher grades.
- ATerra Park LakePolk County · 16.8 mi · Two grade letters higher (D → A)
- CLake PetockaPolk County · 5.3 mi · Higher grade (D → C)
Nearby Lakes in Polk County
Explore Thomas Mitchell Lake across LakeGrade
More Iowa Lake Rankings
Other Grade D Lakes in Iowa
Eutrophic Lakes in Iowa
More records, surveys & data sources
Reservoir Info (USACE NID)
Thomas Mitchell Lake is a man-made reservoir impounded by the Thomas Mitchell Park Dam (completed 1971), built primarily for recreation on the TR-CAMP CREEK; earth-type dam, 27 ft tall and 711 ft long.
- Surface area
- 4.2 ac
- Normal storage
- 25 ac-ft
- Max storage
- 75 ac-ft
- Drainage area
- 0.47 sq mi
- Hazard class
- Significant
- Owner
- Polk County Conservation Board
Source: USACE National Inventory of Dams, NID ID IA00901 · Operator website · Matched by proximity (0.24 km)
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Thomas Mitchell Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 2 facilities have a reported Clean Water Act violation in the past three years.
- Mitchellville City Of StpMitchellville · 2 mi away · NPDES IA0021997MajorRecent violation
- Thomas Mitchell ParkMitchellville · 0.3 mi away · NPDES IA0066966Recent violation
- Altoona, City Of MS4Altoona · 4 mi away · NPDES IA0078603
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: 2024-09-09
Monitoring stations: 1