O'Brien Lake
O'Brien Lake in Crow Wing County, Minnesota has a water quality grade of A (Excellent). Water clarity: 18 ft visibility. Phosphorus: 7.5 µg/L. Chlorophyll-a (algae): 2.1 µg/L.
- Clarity
- 18 ft
- Typical in August
- 72°F
- Type
- Oligotrophic
- Trend
- ↓ Declining
- Public access
- Yes
Next lake in Crow Wing County
O'Brien Lake is a cold, clear oligotrophic lake in Crow Wing County, Minnesota. Water quality is graded A based on 2 sampling years through 2025. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings. Compared to the 84 other monitored lakes in Crow Wing County, O'Brien Lake ranks #48 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-15. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLow algae
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)
Crystal clear, you can see 18 ft down. Phosphorus level: 7.5 µg/L. Chlorophyll-a: 2.1 µg/L. Trophic State Index: 36.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 18 ft | Not graded |
| Phosphorus | 7.5 µg/L | Good |
| Chlorophyll-a (Algae) | 2.1 µg/L | Good |
| Trophic State Index (TSI) | 36 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near O'Brien Lake
Compare lakeside cabins, hotels, and vacation rentals near O'Brien Lake in Crow Wing 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
O'Brien Lake typically sits around 72°F at the surface in August. Summer average is about 71°F. Usually warmest in Jul (about 74°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 34 field readings (2017–2025) via the EPA Water Quality Portal. See the full O'Brien Lake water temperature breakdown →
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Goodrich LakePublic
- O'Brien LakePublic
Fishing O'Brien Lake
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for O'Brien 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 — O'Brien (Northeast Bay)Public Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.169 m/yr | 6 |
| Phosphorus | ↑ Improving | -0.33 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +0.25 µg/L/yr | 6 |
County Ranking
Ranked #48 of 85 lakes in Crow Wing County
Nearby Lakes in Crow Wing County
Frequently asked questions about O'Brien Lake
What is the water quality grade for O'Brien Lake?
- O'Brien Lake in Crow Wing County, Minnesota has a water quality grade of A (Excellent). Water clarity: 18 ft visibility. Phosphorus: 7.5 µg/L. Chlorophyll-a (algae): 2.1 µg/L.
Is O'Brien Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. O'Brien Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 2.1 µg/L. Always check local health department advisories before swimming.
What is the water temperature of O'Brien Lake?
- O'Brien Lake typically sits around 72°F at the surface in August, from 34 EPA Water Quality Portal field readings (2017–2025). That is a typical value for the month, not a live reading.
How deep is O'Brien Lake?
- The available depth estimate for O'Brien Lake is shallower than its measured water clarity, which cannot be right, so no depth is shown.
Are there boat ramps on O'Brien Lake?
- O'Brien Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Goodrich Lake, O'Brien Lake. Public access is listed as yes.
Explore O'Brien Lake across LakeGrade
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Where this data comes from
76 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
MNPCA76 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
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)
Named boat-access points from the USGS National Boat Ramps inventory