Olson Lake
Olson Lake in Washington County, Minnesota has a water quality grade of A (Excellent). Water clarity: 11.2 ft visibility. Phosphorus: 15 µg/L. Chlorophyll-a (algae): 2.6 µg/L. Maximum depth: 15 ft. Surface area: 87.13 acres.
- Clarity
- 11.2 ft
- Typical in August
- 78°F
- Max depth
- 15 ft
- Area
- 87 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- No
Next lake in Washington County
Olson Lake is a 87-acre mesotrophic lake in Washington County, Minnesota with a maximum depth of 15 feet. Water quality is graded A based on 2 sampling years through 2024. Overall water quality is improving over recent sampling years. The lake supports 11 documented fish species including black bullhead, black crappie, and bluegill. No public access — the lake is private or restricted. Compared to the 74 other monitored lakes in Washington County, Olson Lake ranks #12 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-08. Grade methodology: LakeGrade methodology.
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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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Good clarity, visible to about 11.2 ft. Phosphorus level: 15 µg/L. Chlorophyll-a: 2.6 µg/L. Trophic State Index: 42.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11.2 ft | Not graded |
| Phosphorus | 15 µg/L | Good |
| Chlorophyll-a (Algae) | 2.6 µg/L | Good |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Olson Lake
Compare lakeside cabins, hotels, and vacation rentals near Olson 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.
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Water Temperature
Olson Lake typically sits around 78°F at the surface in August. Summer average is about 75°F. Usually warmest in Jul (about 80°F) and coldest in May (about 55°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 83 field readings (2011–2024) via the EPA Water Quality Portal. See the full Olson Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 15 ft |
| Surface Area | 87 acres |
| Shoreline Length | 1.9 mi |
| Littoral Zone | 100% |
| Public Access | No |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Olson Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Water Quality Trend: ↑ Improving
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.155 m/yr | 3 |
EPA Impairment Status
Olson 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 MN82-0101-00 · Official waterbody report · Matched by proximity (0.6 km)
County Ranking
Ranked #12 of 75 lakes in Washington County
Nearby Lakes in Washington County
Frequently asked questions about Olson Lake
What is the water quality grade for Olson Lake?
- Olson Lake in Washington County, Minnesota has a water quality grade of A (Excellent). Water clarity: 11.2 ft visibility. Phosphorus: 15 µg/L. Chlorophyll-a (algae): 2.6 µg/L. Maximum depth: 15 ft. Surface area: 87.13 acres.
Is Olson Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Olson Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 2.6 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Olson Lake?
- Olson Lake typically sits around 78°F at the surface in August, from 83 EPA Water Quality Portal field readings (2011–2024). That is a typical value for the month, not a live reading.
How deep is Olson Lake?
- Olson Lake has a maximum depth of 15 feet. The lake covers 87.13 acres.
What fish are in Olson Lake?
- Fish species found in Olson Lake include black bullhead, black crappie, bluegill, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, yellow bullhead, yellow perch. Olson Lake is located in Washington County, Minnesota.
Explore Olson Lake across LakeGrade
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Moderate nutrients, good water quality
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Where this data comes from
43 measurements from 1 monitoring station, 2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA43 samples · 2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- Analysis of Chlorophyll in Periphyton and Plankton
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder