O'Brien Lake
Itasca County, Minnesota539 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for O'Brien Lake. Here is what has been measured.
- Impaired · Mercury
- 63 ft max depth
- Public access
- Limited data
O'Brien Lake in Itasca County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 13.1 ft visibility. Maximum depth: 63 ft. Surface area: 538.96 acres.
O'Brien Lake is a 539-acre lake in Itasca County, Minnesota with a maximum depth of 63 feet. The lake supports 10 documented fish species including black crappie, bluegill, and bowfin (dogfish). Public access is available.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-09. Methodology: how these readings are compared.
O'Brien Lake covers about 540 acres in Itasca County. If you are planning to stay, you can search lake houses and cabins around O'Brien Lake on Vrbo, or look for a hotel room near the lake on Booking.com or Expedia.
What O'Brien Lake is good for
From access and monitoring records, not editorial picks.
- Clear water13.1 ft of visibility
- Fishing10 species recorded
- Deep water63 ft surveyed max depth
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. O'Brien Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
Whether O'Brien Lake is safe to swim in today is a call for the Minnesota Pollution Control Agency and the Minnesota DNR and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for O'Brien Lake
These are the measurements Minnesota PCA publishes for O'Brien Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Good clarity, visible to about 13.1 ft. TSI 40.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 13.1ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | No reading The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. | |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 40 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about O'Brien Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
O'Brien Lake typically sits around 62°F at the surface in October. Summer average is about 68°F. Usually warmest in Aug (about 71°F) and coldest in May (about 56°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (56°F) to its warmest (71°F).
Typical surface water temperature by month, from 106 field readings (2025–2025) via the EPA Water Quality Portal. See the full O'Brien Lake water temperature breakdown →
Lake Details
Max depth
63 ft
Surface area
539 acres
Shoreline
13.3 mi
Public access
Yes
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
42 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,365 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Stays via Stay22
Stays near O'Brien Lake
Compare lakeside cabins, hotels, and vacation rentals near O'Brien Lake in Itasca 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 O'Brien Lake
Prices for Oct 9–11, 4 adults. Change dates on the map below.
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Fish Species
Click a species to see every lake where it is documented.
Fishing O'Brien Lake
EPA Impairment Status
O'Brien Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Fish consumption.
Source: EPA ATTAINS assessment unit MN31-0032-01 · Official waterbody report
Regulated Pollution Sources Nearby
4 EPA-permitted facilities operate within about 5 miles of O'Brien Lake under Clean Water Act (NPDES) discharge permits. 2 facilities have a reported Clean Water Act violation in the past three years.
- Nashwauk WwtpNashwauk · 2.1 mi away · NPDES MN0053392Recent violation
- Keewatin WwtpKeewatin · 4.3 mi away · NPDES MN0022012Recent violation
- Encore Mineral Resources LlcNashwauk · 1.4 mi away · NPDES MN0020249
- Mesabi Metallics MineNashwauk · 4.9 mi away · NPDES MN0068241
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
Nearby Lakes in Itasca County
Frequently asked questions about O'Brien Lake
Where is O'Brien Lake?
- O'Brien Lake is a lake in Itasca County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of O'Brien Lake?
- O'Brien Lake in Itasca County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 13.1 ft visibility. Maximum depth: 63 ft. Surface area: 538.96 acres.
Is O'Brien Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. O'Brien Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
What is the water temperature of O'Brien Lake?
- O'Brien Lake typically sits around 62°F at the surface in October, from 106 EPA Water Quality Portal field readings (2025–2025). That is a typical value for the month, not a live reading.
How deep is O'Brien Lake?
- O'Brien Lake has a maximum depth of 63 feet. The lake covers 538.96 acres.
What fish are in O'Brien Lake?
- Fish species found in O'Brien Lake include black crappie, bluegill, bowfin (dogfish), hybrid sunfish, largemouth bass, northern pike, pumpkinseed, walleye, yellow bullhead, yellow perch. O'Brien Lake is located in Itasca County, Minnesota.
Can I fish at O'Brien Lake?
- Public access to O'Brien Lake is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Minnesota's fish and wildlife agency, so check its current regulations before you go.
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Where this data comes from
106 measurements from 2 monitoring stations, 2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA106 samples · 2025
Analytical methods
- Field measurement/observation, generic method
Monitoring station identifiers (2)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder