Cedar Lake
Johnson County, Kansas55 acresView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- #6 of 13 in the county
- 29 ft max depth
Cedar Lake in Johnson County, Kansas has a water quality grade of F (Algae-prone). Water clarity: 1.6 ft visibility. Phosphorus: 113 µg/L. Chlorophyll-a (algae): 39.5 µg/L. Surface area: 55 acres.
- Clarity
- 1.6 ft
- Max depth
- ~29 ft est.
- Area
- 55 acres
- Type
- Hypereutrophic
- Phosphorus
- 113 µg/L
- Chlorophyll-a
- 39.5 µg/L
- Trend
- ↓ Declining
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Stays near Cedar Lake
Compare lakeside cabins, hotels, and vacation rentals near Cedar Lake in Johnson County, Kansas — 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.
Top-rated places to stay near Cedar Lake
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Watch Cedar Lake’s letter
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Cedar Lake is a 55-acre highly nutrient-loaded hypereutrophic lake in Johnson County, Kansas with an estimated average depth of about 29 feet. Water quality is graded F based on 2 sampling years through 2021. Overall water quality is declining over recent sampling years. Compared to the 12 other monitored lakes in Johnson County, Cedar Lake ranks #6 for water quality.
Source: EPA Water Quality Portal sampling records, KDHE, last sampled 2021-09-14. 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. Cedar Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 1.6 ft of visibility. Phosphorus 113 µg/L. Chlorophyll-a 39.5 µg/L. TSI 70. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | Not graded |
| Phosphorus | 113 µg/L | Poor |
| Chlorophyll-a (Algae) | 39.5 µg/L | Poor |
| Trophic State Index (TSI) | 70 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~29 ft est. |
| Average Depth | ~9 ft est. |
| Surface Area | 55 acres |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Kansas 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: ↓ Declining
Based on 7 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.093 m/yr | 2 |
| Phosphorus | ↓ Declining | +49.52 µg/L/yr | 7 |
| Chlorophyll-a | ↓ Declining | +1.58 µg/L/yr | 7 |
Reservoir Info (USACE NID)
Cedar Lake is a man-made reservoir impounded by the Cedar Lake (Old Olathe Lake) (completed 1931), built primarily for water supply on the Cedar Creek-Tr; earth-type dam, 39 ft tall and 800 ft long.
- Surface area
- 55 ac
- Normal storage
- 705 ac-ft
- Max storage
- 1,004 ac-ft
- Drainage area
- 5.97 sq mi
- Hazard class
- High
- Owner
- OLATHE, CITY OF
Source: USACE National Inventory of Dams, NID ID KS02489 · Operator website · Matched by proximity (0.46 km)
EPA Impairment Status
Cedar 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 KS-LM061601 · Official waterbody report
County Ranking
Ranked #6 of 13 lakes in Johnson 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 Johnson County
Frequently asked questions about Cedar Lake
Where is Cedar Lake?
- Cedar Lake is a lake in Johnson County, Kansas. 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 Johnson County, Kansas has a water quality grade of F (Algae-prone). Water clarity: 1.6 ft visibility. Phosphorus: 113 µg/L. Chlorophyll-a (algae): 39.5 µg/L. Surface area: 55 acres.
Is Cedar Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Cedar Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
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 55 acres.
Explore Cedar Lake across LakeQuality
More Kansas Lake Rankings
Other Grade F Lakes in Kansas
Hypereutrophic Lakes in Kansas
Where this data comes from
48 measurements from 2 monitoring stations, 2013–2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- EPA R7
EPA_R7_WQX38 samples · 2013–2021 - Kansas Department Of Health And Environment
21KAN001_WQX10 samples · 2013–2017
Analytical methods
- Depth, Secchi disk depth
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Nutrient Analysis
- Chlorophyll a
- Fluorometric Analysis of Chlorophyll a (originally 2334.22A)
Monitoring station identifiers (2)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)