O'Reilly Lake
Itasca County, Minnesota189 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for O'Reilly Lake. Here is what has been measured.
- 79 ft max depth
- Public access
- Limited data
O'Reilly Lake in Itasca County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 16 ft visibility. Maximum depth: 79 ft. Surface area: 189.31 acres.
Minnesota DNR's Targeted Survey on August 17, 2020 caught 0.17 walleye per gill net at O'Reilly Lake. DNR survey details →
O'Reilly Lake is a 189-acre lake in Itasca County, Minnesota with a maximum depth of 79 feet. Overall water quality is declining over recent sampling years. The lake supports 11 documented fish species including black crappie, bluegill, and largemouth bass. Public access is available.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-22. Methodology: how these readings are compared.
What O'Reilly Lake is good for
From access and monitoring records, not editorial picks.
- Clear water16 ft of visibility
- Fishing11 species recorded
- Deep water79 ft surveyed max depth
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether O'Reilly 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'Reilly Lake
These are the measurements Minnesota PCA publishes for O'Reilly Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Crystal clear, you can see 16 ft down. TSI 37.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 16ft | 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. | 37 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about O'Reilly Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
O'Reilly Lake typically sits around 58°F at the surface in October. Summer average is about 72°F. Usually warmest in Jul (about 73°F) and coldest in Oct (about 58°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (58°F) to its warmest (73°F).
Typical surface water temperature by month, from 45 field readings (2022–2025) via the EPA Water Quality Portal. See the full O'Reilly Lake water temperature breakdown →
Minnesota DNR's Targeted Survey on August 17, 2020 caught 0.17 walleye per gill net at O'Reilly Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows O'Reilly Lake’s water-quality measurements separately, and the water-quality trend over 4 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
9 surveys on file from MN DNR Fisheries. Most recent: 2020-08-17 (Targeted Survey).
9 surveys on file · most recent 2020-08-17 (Targeted Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Bluegill | 6.97 | 3–8 in 2020-08-17 | 0.15 lb |
| Bluntnose Minnow | 4.96 | ||
| Largemouth Bass | 4.78 | 9–14 in 2020-08-17 | 0.88 lb |
| Tullibee (Cisco) | 4.17 | 6–8 in 2020-08-17 | 0.25 lb |
CPUE = catch per unit effort, fish caught per net per set in a standardised survey. It measures abundance, not size, and is not a weekly bite report.
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.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —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
Lake Details
Max depth
79 ft
Surface area
189 acres
Shoreline
3.1 mi
Littoral zone
30%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
6 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,302 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Stays via Stay22
Stays near O'Reilly Lake
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Top-rated places to stay near O'Reilly Lake
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Fish Species
Click a species to see every lake where it is documented.
Fishing O'Reilly Lake
Water Quality Trend: Worsening
Based on 4 years of monitoring (2022–2025).
Water clarity
Worsening4 years
Nearby Lakes in Itasca County
Frequently asked questions about O'Reilly Lake
Where is O'Reilly Lake?
- O'Reilly 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'Reilly Lake?
- O'Reilly Lake in Itasca County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 16 ft visibility. Maximum depth: 79 ft. Surface area: 189.31 acres.
Is O'Reilly Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of O'Reilly Lake?
- O'Reilly Lake typically sits around 58°F at the surface in October, from 45 EPA Water Quality Portal field readings (2022–2025). That is a typical value for the month, not a live reading.
How deep is O'Reilly Lake?
- O'Reilly Lake has a maximum depth of 79 feet. The lake covers 189.31 acres.
What fish are in O'Reilly Lake?
- Fish species found in O'Reilly Lake include black crappie, bluegill, largemouth bass, northern pike, pumpkinseed, rock bass, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. O'Reilly Lake is located in Itasca County, Minnesota.
What did the DNR fisheries survey find at O'Reilly Lake?
- Minnesota DNR's Targeted Survey on August 17, 2020 caught 0.17 walleye per gill net at O'Reilly Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows O'Reilly Lake’s water-quality measurements separately, and the water-quality trend over 4 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
Can I fish at O'Reilly Lake?
- Public access to O'Reilly 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
45 measurements from 1 monitoring station, 2022–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA45 samples · 2022–2025
Analytical methods
- Field measurement/observation, generic method
Monitoring station identifiers (1)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder