Oneka Lake
Oneka Lake in Washington County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 4.4 ft visibility.
- Clarity
- 4.4 ft
- Typical in August
- 76°F
- Mean depth
- ~6 ft est.
- Trend
- ↓ Declining
- Public access
- Yes
Next lake in Washington County
Why Oneka Lake has no grade
We grade a lake only when its monitoring record clears the evidence bar: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Oneka Lake, the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. Sampling here has recorded water clarity, but not phosphorus and algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by MPCA and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Oneka Lake is a lake in Washington County, Minnesota with an estimated average depth of about 6 feet. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2023-08-18. Grade methodology: LakeGrade methodology.
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Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Oneka Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Murky, only visible to about 4.4 ft. Trophic State Index: 56.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 4.4 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 56 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Oneka Lake
Compare lakeside cabins, hotels, and vacation rentals near Oneka Lake in Washington County, Minnesota — 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.
Top-rated places to stay near Oneka Lake
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Water Temperature
Oneka Lake typically sits around 76°F at the surface in August. Summer average is about 75°F. Usually warmest in Jul (about 82°F) and coldest in May (about 57°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 18 field readings (2010–2023) via the EPA Water Quality Portal. See the full Oneka Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~6 ft est. |
| Public Access | Yes |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Minnesota has not published bathymetry for Oneka 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.
Recreation & Access
- Oneka Lake ParkPublic
Fishing Oneka Lake
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Oneka Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Public Water Access Sites — OnekaPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.15 m/yr | 2 |
Graded lakes near Oneka Lake
Oneka Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Washington County
Frequently asked questions about Oneka Lake
What is the water quality grade for Oneka Lake?
- Oneka Lake in Washington County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 4.4 ft visibility.
Is Oneka Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Oneka Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
What is the water temperature of Oneka Lake?
- Oneka Lake typically sits around 76°F at the surface in August, from 18 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
How deep is Oneka Lake?
- No published bathymetric survey covers Oneka Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 6 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Are there boat ramps on Oneka Lake?
- Oneka Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Oneka Lake Park. Public access is listed as yes.
Explore Oneka Lake across LakeGrade
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Where this data comes from
8 measurements from 1 monitoring station, 2022–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA8 samples · 2022–2023
Analytical methods
- Field measurement/observation, generic method
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory