Serpent Lake
Serpent Lake in Crow Wing County, Minnesota has a water quality grade of A (Excellent). Water clarity: 25 ft visibility. Phosphorus: 12 µg/L. Chlorophyll-a (algae): 1.6 µg/L. Maximum depth: 65 ft. Surface area: 1116.34 acres.
- Clarity
- 25 ft
- Typical in August
- 67°F
- Max depth
- 65 ft
- Area
- 1,116 acres
- Type
- Oligotrophic
- Trend
- → Stable
- Public access
- Yes
- Ice-out
- Apr 15
- Open water
- 233 days
Next lake in Crow Wing County
Free interactive depth-contour map of Serpent Lake, reaching a maximum surveyed depth of 60 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Serpent Lake is a 1,116-acre cold, clear oligotrophic lake in Crow Wing County, Minnesota with a maximum depth of 65 feet. Water quality is graded A based on 2 sampling years through 2025. The lake supports 17 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 3 public boat landings. Compared to the 84 other monitored lakes in Crow Wing County, Serpent Lake ranks #25 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-17. 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 25 ft down. Phosphorus level: 12 µg/L. Chlorophyll-a: 1.6 µg/L. Trophic State Index: 35.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 25 ft | Not graded |
| Phosphorus | 12 µg/L | Good |
| Chlorophyll-a (Algae) | 1.6 µg/L | Good |
| Trophic State Index (TSI) | 35 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Serpent Lake
Compare lakeside cabins, hotels, and vacation rentals near Serpent Lake in Crow Wing 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.
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Water Temperature
Serpent Lake typically sits around 67°F at the surface in August. Summer average is about 66°F. Usually warmest in Jul (about 68°F) and coldest in May (about 50°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 194 field readings (2011–2025) via the EPA Water Quality Portal. See the full Serpent Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Serpent Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was moderate (26,546 cells/mL) on November 22, 2025.
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 | 65 ft |
| Surface Area | 1,116 acres |
| Shoreline Length | 9 mi |
| Littoral Zone | 30% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Pennington Mine LakePublic
- Portsmouth Mine LakePublic
- Serpent Lake (West)Public
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Serpent 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
11 surveys on file from MN DNR Fisheries. Most recent: 2023-08-21 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluntnose Minnow | 67.90 | — |
| BNS | 21.00 | — |
| Largemouth Bass | 13.69 | 0.68 lb |
| IOD | 13.43 | — |
| MMS | 12.47 | — |
| Bluegill | 12.03 | 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.
Largemouth Bass
Bluegill
From the 2023-08-21 survey
Serpent Lake is a 1,057-acre lake located in Crow Wing County. It spans the cities of Crosby on the west shore and Deerwood on the east. A public access is located in the Crosby city park on the west end. Another access is located just north of Deerwood on the east shore. Serpent reaches depths of 65' with 32% of the…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Serpent Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — SerpentFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Serpent (0012)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — SerpentFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — SerpentPublic 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 | → Stable | +0.084 m/yr | 6 |
| Phosphorus | → Stable | -0.16 µg/L/yr | 6 |
| Chlorophyll-a | → Stable | -0.04 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (19 observations).
Estimated open water season: 233 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2024-03-15 (2024) | 2022-05-05 (2022) |
| Ice-In | 2018-11-20 (2018) | 2024-01-05 (2024) |
Most recent ice-out: 2025-04-15
EPA Impairment Status
Serpent Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN18-0090-00 · Official waterbody report
County Ranking
Ranked #25 of 85 lakes in Crow Wing County
Nearby Lakes in Crow Wing County
Frequently asked questions about Serpent Lake
What is the water quality grade for Serpent Lake?
- Serpent Lake in Crow Wing County, Minnesota has a water quality grade of A (Excellent). Water clarity: 25 ft visibility. Phosphorus: 12 µg/L. Chlorophyll-a (algae): 1.6 µg/L. Maximum depth: 65 ft. Surface area: 1116.34 acres.
Is Serpent Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Serpent Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 1.6 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Serpent Lake?
- Serpent Lake typically sits around 67°F at the surface in August, from 194 EPA Water Quality Portal field readings (2011–2025). That is a typical value for the month, not a live reading.
How deep is Serpent Lake?
- Serpent Lake has a maximum depth of 65 feet. The lake covers 1116.34 acres.
What fish are in Serpent Lake?
- Fish species found in Serpent Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, burbot, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, rock bass, smallmouth bass, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. Serpent Lake is located in Crow Wing County, Minnesota.
When does Serpent Lake thaw?
- Serpent Lake typically has ice-out around Apr 15. Ice typically forms around Dec 4. The open water season is approximately 233 days.
Does Serpent Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Serpent Lake (clouds, ice, or an off-season gap). The most recent reading was moderate (26,546 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Are there boat ramps on Serpent Lake?
- Serpent Lake has 3 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Pennington Mine Lake, Portsmouth Mine Lake, Serpent Lake (West). Public access is listed as yes.
Explore Serpent Lake across LakeGrade
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Where this data comes from
125 measurements from 2 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA125 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (2)
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