Cedar Lake
Madison County, Iowa84 acresView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- #2 of 2 in the county
- 29 ft max depth
Cedar Lake in Madison County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 1.6 ft visibility. Phosphorus: 98 µg/L. Chlorophyll-a (algae): 62.7 µg/L. Surface area: 84 acres.
- Clarity
- 1.6 ft
- Typical in September
- 75°F
- Max depth
- ~29 ft est.
- Area
- 84 acres
- Type
- Hypereutrophic
- Phosphorus
- 98 µg/L
- Chlorophyll-a
- 62.7 µg/L
- Trend
- ↑ Improving
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Stays near Cedar Lake
Compare lakeside cabins, hotels, and vacation rentals near Cedar Lake in Madison 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 Cedar Lake are listed below.
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Watch Cedar Lake’s letter
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Cedar Lake is a 84-acre highly nutrient-loaded hypereutrophic lake in Madison County, Iowa with an estimated average depth of about 29 feet. Water quality is graded F based on 2 sampling years through 2022. Overall water quality is improving over recent sampling years. 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: 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. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 1.6 ft of visibility. Phosphorus 98 µg/L. Chlorophyll-a 62.7 µg/L. TSI 70. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | Not graded |
| Phosphorus | 98 µg/L | Poor |
| Chlorophyll-a (Algae) | 62.7 µg/L | Poor |
| Trophic State Index (TSI) | 70 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Cedar Lake typically sits around 75°F at the surface in September. Summer average is about 77°F. 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 →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~29 ft est. |
| Average Depth | ~16 ft est. |
| Surface Area | 84 acres |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Iowa has not published bathymetry for Cedar Lake.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Fishing Cedar Lake
Water Quality Trend: ↑ Improving
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.05 m/yr | 3 |
| Phosphorus | ↑ Improving | -3.3 µg/L/yr | 3 |
| Chlorophyll-a | ↑ Improving | -9.75 µg/L/yr | 3 |
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)
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.
County Ranking
Ranked #2 of 2 lakes in Madison County
Nearby Lakes With Higher Grades
Cedar Lake holds Grade F. 2 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Madison County
Frequently asked questions about Cedar Lake
Where is Cedar Lake?
- Cedar Lake is a lake in Madison County, Iowa. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Cedar Lake?
- Cedar Lake in Madison County, Iowa has a water quality grade of F (Algae-prone). Water clarity: 1.6 ft visibility. Phosphorus: 98 µg/L. Chlorophyll-a (algae): 62.7 µg/L. Surface area: 84 acres.
Is Cedar Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Cedar Lake?
- Cedar Lake typically sits around 75°F at the surface in September, from 9 EPA Water Quality Portal field readings (2018–2022). That is a typical value for the month, not a live reading.
How deep is Cedar Lake?
- No published bathymetric survey covers Cedar Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 29 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 84 acres.
Explore Cedar Lake across LakeQuality
More Iowa Lake Rankings
Other Grade F Lakes in Iowa
Hypereutrophic Lakes in Iowa
Where this data comes from
36 measurements from 1 monitoring station, 2020–2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Iowa DNR Surface Water Monitoring Data
21IOWA_WQX36 samples · 2020–2022
Analytical methods
- Unknown
- Phosphorus by Colorimetry
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- 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)
Lake size & watershed from HydroLAKES (HydroSHEDS)