O'Leary Lake
O'Leary Lake in Dakota County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 2.6 ft visibility. Phosphorus: 153 µg/L. Chlorophyll-a (algae): 72.3 µg/L. Maximum depth: 33.5 ft. Surface area: 30.55 acres.
- Clarity
- 2.6 ft
- Typical in August
- 72°F
- Max depth
- 33.5 ft
- Area
- 31 acres
- Type
- Hypereutrophic
- Trend
- → Stable
- Public access
- Yes
- Ice-out
- Mar 31
- Open water
- 238 days
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near O'Leary Lake →
Next lake in Dakota County
O'Leary Lake is a 31-acre highly nutrient-loaded hypereutrophic lake in Dakota County, Minnesota with a maximum depth of 34 feet (8-foot average). Water quality is graded F based on 2 sampling years through 2023. Water clarity is improving over recent sampling years. The lake supports 7 documented fish species including black bullhead, black crappie, and bluegill. Public access is available. Compared to the 44 other monitored lakes in Dakota County, O'Leary Lake ranks #32 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2023-09-18. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLimited data
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.
Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom
Water Quality Grade: F (Algae-prone)
Very murky, less than 2.6 ft of visibility. Phosphorus level: 153 µg/L. Chlorophyll-a: 72.3 µg/L. Trophic State Index: 71.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.6 ft | Not graded |
| Phosphorus | 153 µg/L | Poor |
| Chlorophyll-a (Algae) | 72.3 µg/L | Poor |
| Trophic State Index (TSI) | 71 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near O'Leary Lake
Compare lakeside cabins, hotels, and vacation rentals near O'Leary Lake in Dakota 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around O'Leary Lake are listed below.
Top-rated places to stay near O'Leary Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
O'Leary Lake typically sits around 72°F at the surface in August. Summer average is about 75°F. Usually warmest in Jul (about 78°F) and coldest in Sep (about 65°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 13 field readings (2010–2025) via the EPA Water Quality Portal.
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 33.5 ft |
| Average Depth | 8.3 ft |
| Surface Area | 31 acres |
| Shoreline Length | 1.5 mi |
| Littoral Zone | 78% |
| Public Access | Yes |
Fish Species
Click a species to see every graded lake where it is documented.
Fishing O'Leary Lake
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
DNR Fisheries Survey Summary
8 surveys on file from MN DNR Fisheries. Most recent: 2013-07-01 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 45.73 | 0.12 lb |
| Black Bullhead | 15.08 | 0.27 lb |
| Yellow Perch | 9.28 | 0.11 lb |
| Black Crappie | 7.05 | 0.14 lb |
| Northern Pike | 6.60 | 2.72 lb |
| Hybrid Sunfish | 5.67 | 0.14 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
Black Bullhead
Yellow Perch
Black Crappie
From the 2013-07-01 survey
Fish Lake is a 29 acre lake managed by the Fishing in the Neighborhood Program and the City of Eagan. The lake has a boat access (electric motors only), a fishing pier, and shore fishing areas for anglers. The lake supports a diverse fish community and was previously stocked with Channel Catfish from 1998-2002.…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for O'Leary Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — FishFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — FishFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — FishPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.088 m/yr | 6 |
| Phosphorus | → Stable | +0.63 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +1.47 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (9 observations).
Estimated open water season: 238 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2002-03-16 (2002) | 2008-04-17 (2008) |
| Ice-In | 2007-11-21 (2007) | 2005-11-26 (2005) |
Most recent ice-out: 2015-03-29
EPA Impairment Status
O'Leary Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN19-0057-00 · Official waterbody report · Matched by proximity (1.14 km)
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of O'Leary Lake under Clean Water Act (NPDES) discharge permits.
- Fish Lake Alum Treatment FacilityEagan · 0.4 mi away · NPDES MN0069752
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.
County Ranking
Ranked #32 of 45 lakes in Dakota County
Nearby Lakes With Higher Grades
O'Leary Lake holds Grade F. 3 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
Nearby Lakes in Dakota County
Frequently asked questions about O'Leary Lake
What is the water quality grade for O'Leary Lake?
- O'Leary Lake in Dakota County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 2.6 ft visibility. Phosphorus: 153 µg/L. Chlorophyll-a (algae): 72.3 µg/L. Maximum depth: 33.5 ft. Surface area: 30.55 acres.
Is O'Leary Lake safe to swim in?
- Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom. O'Leary Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 72.3 µg/L. Always check local health department advisories before swimming.
What is the water temperature of O'Leary Lake?
- O'Leary Lake typically sits around 72°F at the surface in August, from 13 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
How deep is O'Leary Lake?
- O'Leary Lake has a maximum depth of 33.5 feet and an average depth of 8.3 feet. The lake covers 30.55 acres.
What fish are in O'Leary Lake?
- Fish species found in O'Leary Lake include black bullhead, black crappie, bluegill, hybrid sunfish, largemouth bass, northern pike, yellow perch. O'Leary Lake is located in Dakota County, Minnesota.
When does O'Leary Lake thaw?
- O'Leary Lake typically has ice-out around Mar 31. Ice typically forms around Nov 24. The open water season is approximately 238 days.
Explore O'Leary Lake across LakeGrade
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Where this data comes from
32 measurements from 1 monitoring station, 2020–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA32 samples · 2020–2023
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Turbidity, Nephelometric Method
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
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate