Cedar Lake
Madison County, Iowa84 acresView mapDirections
Iowa DNR publishes the water-quality measurements for Cedar Lake. Here is what has been measured.
- Hypereutrophic
- 29 ft max depth
Cedar Lake in Madison County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. Water clarity: 1.6 ft visibility. Phosphorus: 98 µg/L. Chlorophyll-a (algae): 62.7 µg/L. Surface area: 84 acres.
Cedar Lake is a 84-acre highly nutrient-loaded hypereutrophic lake in Madison County, Iowa with an estimated average depth of about 29 feet. 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. Methodology: how these readings are compared.
Swimming conditions
Readings onlyAlgae risk
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Cedar Lake is safe to swim in today is a call for the Iowa Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Cedar Lake
These are the measurements Iowa DNR publishes for Cedar Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 1.6 ft of visibility. Phosphorus 98 µg/L. Chlorophyll-a 62.7 µg/L. TSI 70.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1.6ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 98µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 62.7µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 70 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Cedar Lake
Answers come straight from the public measurements and survey records on this page.
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.
Column height runs from this lake’s coldest month (71°F) to its warmest (82°F).
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
Max depth
~29 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
Watershed (drainage) area
16 sq mi
HydroLAKES / HydroSHEDS
Shoreline
2.3 mi
HydroLAKES / HydroSHEDS
Elevation
978 ft
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.
Stays via Stay22
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 readings cover nutrients and algae, not lodging. Cabins and rentals around Cedar Lake are listed below.
Top-rated places to stay near Cedar Lake
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Planning a whole trip? See where to stay at Iowa’s top lakes →
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Fishing Cedar Lake
Water quality readings over time
3 seasons of samples on record (2020–2022). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Worsening3 years
Phosphorus
Improving-3.3 µg/L/yr3 years
Chlorophyll-a
Improving-9.75 µg/L/yr3 years
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.
Nearby Lakes in Madison County
Frequently asked questions about Cedar Lake
Where is Cedar Lake?
- Cedar Lake is a lake in Madison County, Iowa. Its water-quality measurements are published by Iowa DNR and shown on this page as reported.
What is the water quality of Cedar Lake?
- Cedar Lake in Madison County, Iowa has water-quality measurements published by Iowa DNR, shown here as reported. 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?
- Nutrient and algae readings are 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
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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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)