Ossawinnamakee Lake
Crow Wing County, Minnesota711 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Ossawinnamakee Lake. Here is what has been measured.
- Oligotrophic
- Impaired · Mercury
- 2 aquatic invasives
- 63 ft max depth
- Public access
Ossawinnamakee Lake in Crow Wing County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 20 ft visibility. Phosphorus: 9 µg/L. Chlorophyll-a (algae): 1.8 µg/L. Maximum depth: 63 ft. Surface area: 711.33 acres.
Minnesota DNR's Targeted Survey on July 25, 2022 caught 24.69 largemouth bass per hour of electrofishing at Ossawinnamakee Lake. Length samples in the latest survey that recorded them ran 3–17 inches. DNR survey details →
Ossawinnamakee Lake is a 711-acre cold, clear oligotrophic lake in Crow Wing County, Minnesota with a maximum depth of 63 feet. Overall water quality is declining over recent sampling years. The lake supports 18 documented fish species including black crappie, bluegill, and bowfin (dogfish). Public access is available. Compared to the 84 other monitored lakes in Crow Wing County, Ossawinnamakee Lake ranks #11 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-15. Methodology: how these readings are compared.
Ossawinnamakee Lake covers about 710 acres in Crow Wing County. The median ice-out date is April 17, which is when the open-water season begins. If you are planning to stay, you can search lake houses and cabins around Ossawinnamakee Lake on Vrbo, or look for a hotel room near the lake on Booking.com or Expedia.
What Ossawinnamakee Lake is good for
From access and monitoring records, not editorial picks.
- Clear water20 ft of visibility
- Fishing18 species recorded
- Ice seasonIce-out around Apr 17
- Deep water63 ft surveyed max depth
Swimming conditions
Readings onlyLow algae
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Ossawinnamakee Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
Whether Ossawinnamakee 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 Ossawinnamakee Lake
These are the measurements Minnesota PCA publishes for Ossawinnamakee 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 20 ft down. Phosphorus 9 µg/L. Chlorophyll-a 1.8 µg/L. TSI 35.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 20ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 9µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 1.8µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 35 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Ossawinnamakee Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Ossawinnamakee Lake typically sits around 70°F at the surface in September. Summer average is about 62°F. Usually warmest in Jun (about 70°F) and coldest in Aug (about 57°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (57°F) to its warmest (70°F).
Typical surface water temperature by month, from 92 field readings (2017–2025) via the EPA Water Quality Portal. See the full Ossawinnamakee Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Ossawinnamakee Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (188,799 cells/mL) on November 23, 2024.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Minnesota DNR's Targeted Survey on July 25, 2022 caught 24.69 largemouth bass per hour of electrofishing at Ossawinnamakee Lake. Length samples in the latest survey that recorded them ran 3–17 inches.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Ossawinnamakee Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
12 surveys on file from MN DNR Fisheries. Most recent: 2025-08-06 (Targeted Survey).
12 surveys on file · most recent 2025-08-06 (Targeted Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Bluntnose Minnow | 36.11 | ||
| Bluegill | 25.08 | 2–7 in 2021-06-21 | 0.09 lb |
| Largemouth Bass | 22.67 | 3–17 in 2021-06-21 | 0.93 lb |
| Tullibee (Cisco) | 6.74 | 7–15 in 2021-06-21 | 1.03 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 2025-08-06 survey
Temperature and dissolved oxygen (DO) measurements were collected from the deepest basin in Ossawinnamakee Lake on August 6th, 2025, to evaluate the quantity and quality of cold, oxygenated water (i.e., oxythermal habitat) available to Cisco, also known as Tullibee, the most sensitive coldwater species present in this…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Ossawinnamakee Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — OssawinnamakeeFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Ossawinnamakee (0184)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — OssawinnamakeeFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — OssawinnamakeePublic Water Access Sites · MN DNR LakeFinder
Lake Details
Max depth
63 ft
Surface area
711 acres
Shoreline
13.3 mi
Littoral zone
32%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
48 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,201 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Stays via Stay22
Stays near Ossawinnamakee Lake
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Fish Species
Click a species to see every lake where it is documented.
Fishing Ossawinnamakee Lake
- → Ossawinnamakee Lake fishing: DNR survey catch rates, species & stocking
- → Ossawinnamakee Lake fishing forecast & best times (species outlook + 14-day solunar calendar)
- → Ossawinnamakee Lake fishing regulations (limits, seasons, special rules)
- → Is it safe to eat fish from Ossawinnamakee Lake? (mercury & PFAS guide)
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Water Quality Trend: Worsening
Based on 6 years of monitoring (2020–2025).
Water clarity
Stable6 years
Phosphorus
Worsening+0.5 µg/L/yr6 years
Chlorophyll-a
Worsening+0.2 µg/L/yr6 years
Ice season
Typical ice-out
Apr 17
Earliest Mar 22, 2024 · Latest May 12, 2013
Typical ice-in
Nov 29
Earliest Nov 10, 1991 · Latest Dec 14, 2004
Most recent ice-out
Mar 22
2024
71 observations · Minnesota PCA ice records
Reservoir Info (USACE NID)
Ossawinnamakee Lake is a man-made reservoir impounded by the Lake Ossawinnamakee (completed 1937), built primarily for recreation on the Pelican Brook; gravity-type dam, 10 ft tall and 48 ft long.
- Surface area
- 662 ac
- Normal storage
- 8,812 ac-ft
- Max storage
- 10,744 ac-ft
- Drainage area
- 47.2 sq mi
- Hazard class
- Low
- Owner
- MNDNR
Source: USACE National Inventory of Dams, NID ID MN00047 · Operator website
EPA Impairment Status
Ossawinnamakee 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 MN18-0352-00 · Official waterbody report
Nearby Lakes in Crow Wing County
Frequently asked questions about Ossawinnamakee Lake
Where is Ossawinnamakee Lake?
- Ossawinnamakee Lake is a lake in Crow Wing County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Ossawinnamakee Lake?
- Ossawinnamakee Lake in Crow Wing County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 20 ft visibility. Phosphorus: 9 µg/L. Chlorophyll-a (algae): 1.8 µg/L. Maximum depth: 63 ft. Surface area: 711.33 acres.
Is Ossawinnamakee Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Ossawinnamakee 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 Ossawinnamakee Lake?
- Ossawinnamakee Lake typically sits around 70°F at the surface in September, from 92 EPA Water Quality Portal field readings (2017–2025). That is a typical value for the month, not a live reading.
How deep is Ossawinnamakee Lake?
- Ossawinnamakee Lake has a maximum depth of 63 feet. The lake covers 711.33 acres.
What fish are in Ossawinnamakee Lake?
- Fish species found in Ossawinnamakee Lake include black crappie, bluegill, bowfin (dogfish), brown bullhead, greater redhorse, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, rock bass, shorthead redhorse, smallmouth bass, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. Ossawinnamakee Lake is located in Crow Wing County, Minnesota.
What did the DNR fisheries survey find at Ossawinnamakee Lake?
- Minnesota DNR's Targeted Survey on July 25, 2022 caught 24.69 largemouth bass per hour of electrofishing at Ossawinnamakee Lake. Length samples in the latest survey that recorded them ran 3–17 inches. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Ossawinnamakee Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
When does Ossawinnamakee Lake thaw?
- Ossawinnamakee Lake typically has ice-out around Apr 17. Ice typically forms around Nov 29. The open water season is approximately 226 days.
Does Ossawinnamakee Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Ossawinnamakee Lake (clouds, ice, or an off-season gap). The most recent reading was high (188,799 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Can I fish at Ossawinnamakee Lake?
- Public access to Ossawinnamakee 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
86 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA86 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate