Ossawinnamakee Lake
Ossawinnamakee Lake in Crow Wing County, Minnesota has a water quality grade of A (Excellent). 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.
- Clarity
- 20 ft
- Typical in August
- 57°F
- Max depth
- 63 ft
- Area
- 711 acres
- Type
- Oligotrophic
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Apr 17
- Open water
- 226 days
Next lake in Crow Wing County
Ossawinnamakee Lake is a 711-acre cold, clear oligotrophic lake in Crow Wing County, Minnesota with a maximum depth of 63 feet. Water quality is graded A based on 2 sampling years through 2025. 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 with 1 public boat landing. 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. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLow algae
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.
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A (Excellent)
Crystal clear, you can see 20 ft down. Phosphorus level: 9 µg/L. Chlorophyll-a: 1.8 µg/L. Trophic State Index: 35.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 20 ft | Not graded |
| Phosphorus | 9 µg/L | Good |
| Chlorophyll-a (Algae) | 1.8 µg/L | Good |
| Trophic State Index (TSI) | 35 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Ossawinnamakee Lake
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Water Temperature
Ossawinnamakee Lake typically sits around 57°F at the surface in August. 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.
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 ↗
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 63 ft |
| Surface Area | 711 acres |
| Shoreline Length | 13.3 mi |
| Littoral Zone | 32% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Strawberry LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Ossawinnamakee 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
12 surveys on file from MN DNR Fisheries. Most recent: 2025-08-06 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluntnose Minnow | 36.11 | — |
| Bluegill | 25.08 | 0.09 lb |
| Largemouth Bass | 22.67 | 0.93 lb |
| BNS | 10.60 | — |
| JND | 7.13 | — |
| Tullibee (Cisco) | 6.74 | 1.03 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 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
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.061 m/yr | 6 |
| Phosphorus | ↓ Declining | +0.5 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +0.2 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (71 observations).
Estimated open water season: 226 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2024-03-22 (2024) | 2013-05-12 (2013) |
| Ice-In | 1991-11-10 (1991) | 2004-12-14 (2004) |
Most recent ice-out: 2024-03-22
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
Source: EPA ATTAINS assessment unit MN18-0352-00 · Official waterbody report
County Ranking
Ranked #11 of 85 lakes in Crow Wing County
Nearby Lakes in Crow Wing County
Frequently asked questions about Ossawinnamakee Lake
What is the water quality grade for Ossawinnamakee Lake?
- Ossawinnamakee Lake in Crow Wing County, Minnesota has a water quality grade of A (Excellent). 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?
- Excellent for swimming, crystal clear water with minimal algae. Ossawinnamakee Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 1.8 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Ossawinnamakee Lake?
- Ossawinnamakee Lake typically sits around 57°F at the surface in August, 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.
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.
Are there boat ramps on Ossawinnamakee Lake?
- Ossawinnamakee Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Strawberry Lake. Public access is listed as yes.
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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)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate