Windmill Lake is a 25-acre productive, nutrient-rich eutrophic lake in Taylor 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 3 other monitored lakes in Taylor County, Windmill Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2024-10-01. Grade methodology: LakeGrade methodology.
Watch Windmill Lake water quality
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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 2.5 ft of visibility. Chlorophyll-a: 33.9 µg/L. Trophic State Index: 65.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.5 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 33.9 µg/L | F |
| Trophic State Index (TSI) | 65 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 25 acres |
Where to stay near Windmill Lake
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Fishing Windmill Lake
Water Quality Trend: ↓ Declining
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.237 m/yr | 4 |
| Chlorophyll-a | ↓ Declining | +15.62 µg/L/yr | 4 |
Water Temperature
Windmill Lake averages about 80°F at the surface in summer, usually warmest in Jul (about 83°F) and coldest in Sep (about 73°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 31 field readings (2010–2023) via the EPA Water Quality Portal. See the full Windmill Lake water temperature breakdown →
Location & Depth Map
Free interactive depth-contour map of Windmill Lake, reaching a maximum surveyed depth of 16 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Iowa DNR.
County Ranking
Ranked #4 of 4 lakes in Taylor County
Cleaner Lakes Within 30 Miles
Windmill Lake holds Grade F. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Taylor County
Explore Windmill Lake across LakeGrade
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Eutrophic Lakes in Iowa
More records, surveys & data sources
Reservoir Info (USACE NID)
Windmill Lake is a man-made reservoir impounded by the Windmill Lake Dam (completed 1969), built primarily for recreation on the TR-WEST BRANCH 102 RIVER; earth-type dam, 35 ft tall and 900 ft long.
- Surface area
- 24.5 ac
- Normal storage
- 66 ac-ft
- Max storage
- 247 ac-ft
- Drainage area
- 0.84 sq mi
- Hazard class
- Low
- Owner
- Taylor County Conservation Board
Source: USACE National Inventory of Dams, NID ID IA01053 · Operator website
EPA Impairment Status
Windmill Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IA 05-PLA-1482 · Official waterbody report
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Windmill Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- New Market City Of StpNew Market · 3.3 mi away · NPDES IA0033049Recent violation
- Gravity, City Of (Southern Iowa Rural Water Assn.)Gravity · 3.5 mi away · NPDES IA0075957
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
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2024-10-01
Monitoring stations: 1