Oak Lake
Oak Lake in Polk County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 3 ft visibility. Phosphorus: 113 µg/L. Chlorophyll-a (algae): 30.7 µg/L.
- Clarity
- 3 ft
- Mean depth
- ~11 ft est.
- Type
- Eutrophic
- Trend
- ↑ Improving
- Public access
- No
- Ice-out
- Apr 12
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Oak Lake →
Next lake in Polk County
Oak Lake is a productive, nutrient-rich eutrophic lake in Polk County, Minnesota with an estimated average depth of about 11 feet. Water quality is graded F based on 2 sampling years through 2025. Overall water quality is improving over recent sampling years. Limited fish-species data available. No public access — the lake is private or restricted. Compared to the 18 other monitored lakes in Polk County, Oak Lake ranks #17 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-23. Grade methodology: LakeGrade methodology.
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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.
Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom
Water Quality Grade: F (Algae-prone)
Very murky, less than 3 ft of visibility. Phosphorus level: 113 µg/L. Chlorophyll-a: 30.7 µg/L. Trophic State Index: 66.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3 ft | Not graded |
| Phosphorus | 113 µg/L | Poor |
| Chlorophyll-a (Algae) | 30.7 µg/L | Poor |
| Trophic State Index (TSI) | 66 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Oak Lake
Compare lakeside cabins, hotels, and vacation rentals near Oak Lake in Polk 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Oak Lake are listed below.
Top-rated places to stay near Oak Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Oak Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (469,894 cells/mL) on July 19, 2026.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~11 ft est. |
| Public Access | No |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Minnesota has not published bathymetry for Oak 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 Oak Lake
Water Quality Trend: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.029 m/yr | 6 |
| Phosphorus | ↑ Improving | -32.71 µg/L/yr | 6 |
| Chlorophyll-a | ↑ Improving | -11.77 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (11 observations).
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2012-03-20 (2012) | 2013-05-08 (2013) |
| Ice-In | 2017-11-06 (2017) | 2017-11-06 (2017) |
Most recent ice-out: 2020-04-27
County Ranking
Ranked #17 of 19 lakes in Polk County
Nearby Lakes With Higher Grades
Oak Lake holds Grade F. 3 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 Polk County
Frequently asked questions about Oak Lake
What is the water quality grade for Oak Lake?
- Oak Lake in Polk County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 3 ft visibility. Phosphorus: 113 µg/L. Chlorophyll-a (algae): 30.7 µg/L.
Is Oak Lake safe to swim in?
- Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom. Oak Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 30.7 µg/L. Always check local health department advisories before swimming.
How deep is Oak Lake?
- No published bathymetric survey covers Oak Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 11 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
When does Oak Lake thaw?
- Oak Lake typically has ice-out around Apr 12.
Does Oak Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Oak Lake (clouds, ice, or an off-season gap). The most recent reading was high (469,894 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Explore Oak Lake across LakeGrade
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Where this data comes from
87 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA87 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent 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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate