Thomas Mitchell Lake
Polk County, Iowa4 acresView mapDirections
Nutrients and algae sit mid-range for this region.
↑ up from D at the last regrade
- Eutrophic
- #3 of 12 in the county
Thomas Mitchell Lake in Polk County, Iowa has a water quality grade of C (Fair). Water clarity: 3.3 ft visibility. Phosphorus: 87 µg/L. Chlorophyll-a (algae): 13.2 µg/L. Surface area: 4.2 acres.
- Clarity
- 3.3 ft
- Area
- 4 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
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Stays near Thomas Mitchell Lake
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Watch Thomas Mitchell Lake’s letter
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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.
Thomas Mitchell Lake is a 4-acre productive, nutrient-rich eutrophic lake in Polk County, Iowa. Water quality is graded C based on 2 sampling years through 2024. Overall water quality 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: LakeQuality methodology.
Swimming Safety
Grade onlyModerate
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: C (Fair)
Very murky, less than 3.3 ft of visibility. Phosphorus 87 µg/L. Chlorophyll-a 13.2 µg/L. TSI 61. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.3 ft | Not graded |
| Phosphorus | 87 µg/L | Poor |
| Chlorophyll-a (Algae) | 13.2 µg/L | Good |
| Trophic State Index (TSI) | 61 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 4 acres |
No bathymetric survey has been published for Thomas Mitchell Lake, so its depth is not documented here.
Fishing Thomas Mitchell Lake
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.06 m/yr | 2 |
| Phosphorus | ↓ Declining | +27 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -11.5 µg/L/yr | 2 |
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.
County Ranking
Ranked #3 of 12 lakes in Polk County
Nearby Lakes With Higher Grades
Thomas Mitchell Lake holds Grade C. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Polk County
Frequently asked questions about Thomas Mitchell Lake
Where is Thomas Mitchell Lake?
- Thomas Mitchell Lake is a lake in Polk County, Iowa. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Thomas Mitchell Lake?
- Thomas Mitchell Lake in Polk County, Iowa has a water quality grade of C (Fair). Water clarity: 3.3 ft visibility. Phosphorus: 87 µg/L. Chlorophyll-a (algae): 13.2 µg/L. Surface area: 4.2 acres.
Is Thomas Mitchell Lake safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Explore Thomas Mitchell Lake across LakeQuality
More Iowa Lake Rankings
Other Grade C Lakes in Iowa
Eutrophic Lakes in Iowa
Where this data comes from
32 measurements from 1 monitoring station, 2023–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Iowa DNR Surface Water Monitoring Data
21IOWA_WQX32 samples · 2023–2024
Analytical methods
- Unknown
- Phosphorus by Colorimetry
- In-Vitro Determination of Chlorophyll
- ISU modification of APHA 2130-B
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)