O'Brien Lake
O'Brien Lake in Itasca County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 13.1 ft visibility. Maximum depth: 63 ft. Surface area: 538.96 acres.
- Clarity
- 13.1 ft
- Typical in August
- 71°F
- Max depth
- 63 ft
- Area
- 539 acres
- Public access
- Yes
Next lake in Itasca County
Why O'Brien 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 O'Brien 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.
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 with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-09. 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 O'Brien Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Good clarity, visible to about 13.1 ft. Trophic State Index: 40.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 13.1 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 40 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay 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
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Water Temperature
O'Brien Lake typically sits around 71°F at the surface in August. 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.
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
| Characteristic | Value |
|---|---|
| Maximum Depth | 63 ft |
| Surface Area | 539 acres |
| Shoreline Length | 13.3 mi |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- O'Brien ReservoirPublic
Fish Species
Click a species to see every graded 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
Source: EPA ATTAINS assessment unit MN31-0032-02 · Official waterbody report · Matched by proximity (0.47 km)
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.
Graded lakes near O'Brien Lake
O'Brien Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Itasca County
Frequently asked questions about O'Brien Lake
What is the water quality grade for O'Brien Lake?
- O'Brien Lake in Itasca County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 13.1 ft visibility. Maximum depth: 63 ft. Surface area: 538.96 acres.
Is O'Brien Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. O'Brien 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 O'Brien Lake?
- O'Brien Lake typically sits around 71°F at the surface in August, 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.
Are there boat ramps on O'Brien Lake?
- O'Brien Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include O'Brien Reservoir. Public access is listed as yes.
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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)
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory