O'Reilly Lake
Itasca County, MinnesotaLimited DataOligotrophic
O'Reilly Lake earns an A — every scored parameter (clarity) rates among the best monitored waters in Itasca County.
The lake's low TSI puts it in oligotrophic territory — the cleanest of the four trophic classes, but also the most vulnerable to nutrient-driven shifts. The lake's 79 ft maximum depth is in the upper tier for Minnesota — deep enough for cold-water fish to find refuge in summer. O'Reilly Lake covers 189 acres alongside 3.1 miles of shoreline — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. O'Reilly Lake ranks 34 of 141 in Itasca County, putting it in the upper tier of locally monitored lakes.
No invasive species are currently listed at O'Reilly Lake — the lake remains off the Minnesota infested-waters roster. The fishery includes walleye among the lake's 11 documented species — a notable draw for Minnesota anglers. A documented public access point at O'Reilly Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-26. Grade methodology: LakeGrade methodology.
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Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Crystal clear, you can see 16 ft down. Trophic State Index: 37.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 16 ft | A |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 37 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 79 ft |
| Surface Area | 189.31 acres |
| Shoreline Length | 3.1 mi |
| Littoral Zone | 30% |
| Public Access | Yes |
Fish Species
Click a species to see all Minnesota and Wisconsin lakes where it is found.
→ Best fishing times for O'Reilly Lake (14-day solunar calendar)
→ Is it safe to eat fish from O'Reilly Lake? (mercury & PFAS guide)
→ O'Reilly Lake fishing regulations (limits, seasons, special rules)
Water Quality Trend: → Stable
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.08 m/yr | 3 |
Location
County Ranking
Ranked #34 of 141 lakes in Itasca County
Nearby Lakes in Itasca County
More Minnesota Lake Rankings
State Parks Near O'Reilly Lake
Other Grade A Lakes in Minnesota
Oligotrophic Lakes in Minnesota
DNR Fisheries Survey Summary
9 surveys on file from MN DNR Fisheries. Most recent: 2020-08-17 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| CNM | 25.23 | — |
| Bluegill | 6.97 | 0.15 lb |
| IOD | 5.52 | — |
| Bluntnose Minnow | 4.96 | — |
| Largemouth Bass | 4.78 | 0.88 lb |
| Tullibee (Cisco) | 4.17 | 0.25 lb |
CPUE = catch per unit effort, averaged across surveys (excludes juvenile shoreline seining). Higher CPUE = more abundant in standardized sampling.
Length Distributions
Number of fish caught at each inch class in the most recent survey that recorded lengths. Red dashed line marks an approximate trophy threshold for that species.
Bluegill
Largemouth Bass
Tullibee (Cisco)
From the 2020-08-17 survey
The 2012 lake management plan (LMP) indicated Largemouth Bass and Northern Pike were the primary management species while Black Crappie and Bluegill were secondary. The LMP goals were to maintain a Northern Pike catch at 5.0/gill net with 60 and 10% of the fish longer than 21 and 28 inches; maintain the gill-net catch…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for O'Reilly Lake. 4 reports on file.
- —Fisheries Lake Survey — O'ReillyFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — O'Reilly (0588)Aquatic Plant Report · MN DNR LakeFinder
- —Aquatic Plant Report — O'Reilly (2043)Aquatic Plant Report · MN DNR LakeFinder
- —Public Water Access Sites — O'ReillyPublic Water Access Sites · MN DNR LakeFinder
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Lake details from Minnesota DNR LakeFinder
Most recent sample: 2024-09-26
Monitoring stations: 1