Windmill Lake
Taylor County, Iowa25 acresView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- Impaired · Turbidity
- #4 of 4 in the county
Windmill Lake in Taylor County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 2.5 ft visibility. Phosphorus: 94 µg/L. Chlorophyll-a (algae): 33.9 µg/L. Surface area: 24.5 acres.
- Clarity
- 2.5 ft
- Typical in September
- 73°F
- Area
- 25 acres
- Type
- Hypereutrophic
- Phosphorus
- 94 µg/L
- Chlorophyll-a
- 33.9 µg/L
- Trend
- ↓ Declining
Stays via Stay22
Stays near Windmill Lake
Compare lakeside cabins, hotels, and vacation rentals near Windmill Lake in Taylor County, Iowa — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Windmill Lake are listed below.
Top-rated places to stay near Windmill Lake
Prices for Sep 11–13, 4 adults. Change dates on the map below.
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Watch Windmill Lake’s letter
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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.
Windmill Lake is a 25-acre highly nutrient-loaded hypereutrophic 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: LakeQuality methodology.
Swimming Safety
Grade onlyAlgae risk
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 F is nutrients and algae, not a swimming clearance. Windmill Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for turbidity. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 2.5 ft of visibility. Phosphorus 94 µg/L. Chlorophyll-a 33.9 µg/L. TSI 66. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.5 ft | Not graded |
| Phosphorus | 94 µg/L | Poor |
| Chlorophyll-a (Algae) | 33.9 µg/L | Poor |
| Trophic State Index (TSI) | 66 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Windmill Lake typically sits around 73°F at the surface in September. Summer average is about 80°F. 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 →
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 25 acres |
No bathymetric survey has been published for Windmill Lake, so its depth is not documented here.
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 |
| Phosphorus | ↓ Declining | +10 µg/L/yr | 4 |
| Chlorophyll-a | ↓ Declining | +15.62 µg/L/yr | 4 |
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.
County Ranking
Ranked #4 of 4 lakes in Taylor County
Nearby Lakes With Higher Grades
Windmill Lake holds Grade F. 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 Taylor County
Frequently asked questions about Windmill Lake
Where is Windmill Lake?
- Windmill Lake is a lake in Taylor County, Iowa. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Windmill Lake?
- Windmill Lake in Taylor County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 2.5 ft visibility. Phosphorus: 94 µg/L. Chlorophyll-a (algae): 33.9 µg/L. Surface area: 24.5 acres.
Is Windmill Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Windmill Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for turbidity. Check local advisories before you swim.
What is the water temperature of Windmill Lake?
- Windmill Lake typically sits around 73°F at the surface in September, from 31 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
Explore Windmill Lake across LakeQuality
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Hypereutrophic Lakes in Iowa
Where this data comes from
48 measurements from 1 monitoring station, 2021–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Iowa DNR Surface Water Monitoring Data
21IOWA_WQX48 samples · 2021–2024
Analytical methods
- Unknown
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- 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
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)