Cedar Lake is a 84-acre highly nutrient-loaded hypereutrophic lake in Madison County, Iowa. Water quality is graded F based on 2 sampling years through 2022. Water clarity is declining over recent sampling years. Limited fish-species data available. Public access is available. Compared to the 1 other monitored lakes in Madison County, Cedar Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Iowa DNR, last sampled 2022-09-07. 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: 62.7 µg/L. Trophic State Index: 71.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 62.7 µg/L | F |
| Trophic State Index (TSI) | 71 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 84 acres |
| Public Access | Yes |
Where to stay near Cedar Lake
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Fishing Cedar Lake
Water Quality Trend: → Stable
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.05 m/yr | 3 |
| Chlorophyll-a | ↑ Improving | -9.75 µg/L/yr | 3 |
Water Temperature
Cedar Lake averages about 77°F at the surface in summer, usually warmest in Jul (about 82°F) and coldest in Jun (about 71°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 9 field readings (2018–2022) via the EPA Water Quality Portal. See the full Cedar Lake water temperature breakdown →
Location
County Ranking
Ranked #2 of 2 lakes in Madison County
Cleaner Lakes Within 30 Miles
Cedar Lake holds Grade F. 2 nearby lakes hold higher grades.
- BDale Maffitt ReservoirDallas County · 14.6 mi · Two grade letters higher (F → B)
- DHooper Pond LakeWarren County · 22 mi · Higher grade (F → D)
Nearby Lakes in Madison County
Explore Cedar 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)
Cedar Lake is a man-made reservoir impounded by the Cedar Creek Dam (completed 1939), built primarily for water supply on the TR-CEDAR CREEK; earth-type dam, 50 ft tall and 860 ft long.
- Surface area
- 84 ac
- Normal storage
- 935 ac-ft
- Max storage
- 1,820 ac-ft
- Drainage area
- 16.72 sq mi
- Hazard class
- Significant
- Owner
- Winterset Water Works
Source: USACE National Inventory of Dams, NID ID IA01360 · Operator website · Matched by proximity (0.19 km)
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Cedar 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.
- Winterset City Of StpWinterset · 3.5 mi away · NPDES IA0034291MajorRecent violation
- Winterset Water Treatment PlantWinterset · 0.6 mi away · NPDES IA0079961Recent 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)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2022-09-07
Monitoring stations: 1