Olathe Lake
Johnson County, Kansas55 acresView mapDirections
Nutrients and algae sit mid-range for this region.
- Eutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- #2 of 13 in the county
- Limited data
Olathe Lake in Johnson County, Kansas has a water quality grade of C (Fair). Water clarity: 3 ft visibility. Phosphorus: 50 µg/L. Chlorophyll-a (algae): 14.2 µg/L. Surface area: 55 acres.
- Clarity
- 3 ft
- Area
- 55 acres
- Type
- Eutrophic
- Phosphorus
- 50 µg/L
- Chlorophyll-a
- 14.2 µg/L
- Trend
- ↑ Improving
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Watch Olathe Lake’s letter
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Olathe Lake is a 55-acre productive, nutrient-rich eutrophic lake in Johnson County, Kansas. Water quality is graded C based on 2 sampling years through 2018. Overall water quality is improving over recent sampling years. Compared to the 12 other monitored lakes in Johnson County, Olathe Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, KDHE, last sampled 2018-09-17. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLimited data
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 C is nutrients and algae, not a swimming clearance. Olathe 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: C (Fair)
Very murky, less than 3 ft of visibility. Phosphorus 50 µg/L. Chlorophyll-a 14.2 µg/L. TSI 59. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3 ft | Not graded |
| Phosphorus | 50 µg/L | Fair |
| Chlorophyll-a (Algae) | 14.2 µg/L | Fair |
| Trophic State Index (TSI) | 59 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 55 acres |
No bathymetric survey has been published for Olathe Lake, so its depth is not documented here.
Fishing Olathe Lake
Water Quality Trend: ↑ Improving
Based on 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.482 m/yr | 3 |
| Phosphorus | → Stable | -0.22 µg/L/yr | 5 |
| Chlorophyll-a | → Stable | +0.22 µg/L/yr | 5 |
Reservoir Info (USACE NID)
Olathe 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
EPA Impairment Status
Olathe 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-LM061301 · Official waterbody report · Matched by proximity (0.88 km)
County Ranking
Ranked #2 of 13 lakes in Johnson County
Nearby Lakes in Johnson County
Frequently asked questions about Olathe Lake
Where is Olathe Lake?
- Olathe Lake is a lake in Johnson County, Kansas. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Olathe Lake?
- Olathe Lake in Johnson County, Kansas has a water quality grade of C (Fair). Water clarity: 3 ft visibility. Phosphorus: 50 µg/L. Chlorophyll-a (algae): 14.2 µg/L. Surface area: 55 acres.
Is Olathe Lake safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Olathe Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Explore Olathe Lake across LakeQuality
More Kansas Lake Rankings
Other Grade C Lakes in Kansas
Eutrophic Lakes in Kansas
Where this data comes from
60 measurements from 1 monitoring station, 2015–2018. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS Kansas Water Science Center
USGS-KS60 samples · 2015–2018
Analytical methods
- Phosphorus, wu, microKJ ASF, H+
- Plant pigments, sonication & 445
- Pigments, algae, EPA445.0 w/ACTN
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