New Olathe Lake
Johnson County, Kansas165 acresView mapDirections
Clarity, phosphorus, and algae sit in the clean band for this region.
↑ up from C at the last regrade
- Eutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- #1 of 13 in the county
- Limited data
New Olathe Lake in Johnson County, Kansas has a water quality grade of B (Good). Water clarity: 3.4 ft visibility. Phosphorus: 29 µg/L. Chlorophyll-a (algae): 10 µg/L. Surface area: 165 acres.
- Clarity
- 3.4 ft
- Area
- 165 acres
- Type
- Eutrophic
- Phosphorus
- 29 µg/L
- Chlorophyll-a
- 10 µg/L
- Trend
- ↑ Improving
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Watch New Olathe Lake’s letter
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New Olathe Lake is a 165-acre productive, nutrient-rich eutrophic lake in Johnson County, Kansas. Water quality is graded B based on 1 sampling years through 2018. Overall water quality is improving over recent sampling years. Compared to the 12 other monitored lakes in Johnson County, New Olathe Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, KDHE, last sampled 2018-08-06. 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 B is nutrients and algae, not a swimming clearance. New 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: B (Good)
Murky, only visible to about 3.4 ft. Phosphorus 29 µg/L. Chlorophyll-a 10 µg/L. TSI 55. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.4 ft | Not graded |
| Phosphorus | 29 µg/L | Not graded |
| Chlorophyll-a (Algae) | 10 µg/L | Good |
| Trophic State Index (TSI) | 55 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 165 acres |
No bathymetric survey has been published for New Olathe Lake, so its depth is not documented here.
Fishing New 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)
New Olathe Lake is a man-made reservoir impounded by the (New) Olathe Lake (completed 1955), built primarily for water supply on the Cedar Creek; earth-type dam, 69 ft tall and 1,350 ft long.
- Surface area
- 165 ac
- Normal storage
- 3,330 ac-ft
- Max storage
- 5,626 ac-ft
- Drainage area
- 16.9 sq mi
- Hazard class
- High
- Owner
- OLATHE, CITY OF
Source: USACE National Inventory of Dams, NID ID KS02490 · Operator website
EPA Impairment Status
New 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
County Ranking
Ranked #1 of 13 lakes in Johnson County
Nearby Lakes in Johnson County
Frequently asked questions about New Olathe Lake
Where is New Olathe Lake?
- New Olathe Lake is a lake in Johnson County, Kansas. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for New Olathe Lake?
- New Olathe Lake in Johnson County, Kansas has a water quality grade of B (Good). Water clarity: 3.4 ft visibility. Phosphorus: 29 µg/L. Chlorophyll-a (algae): 10 µg/L. Surface area: 165 acres.
Is New Olathe Lake safe to swim in?
- The B is nutrients and algae, not a swimming clearance. New Olathe Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Explore New Olathe Lake across LakeQuality
More Kansas Lake Rankings
Other Grade B Lakes in Kansas
Eutrophic Lakes in Kansas
Where this data comes from
7 measurements from 1 monitoring station, 2013–2018. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Kansas Department Of Health And Environment
21KAN001_WQX7 samples · 2013–2018
Analytical methods
- Depth, Secchi disk depth
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
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