Boy Lake
Cass County, Minnesota3,308 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Boy Lake. Here is what has been measured.
- Mesotrophic
- zebra mussel
- 45 ft max depth
- Public access
Boy Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 10.5 ft visibility. Phosphorus: 21 µg/L. Chlorophyll-a (algae): 6.3 µg/L. Maximum depth: 45 ft. Surface area: 3307.75 acres.
Minnesota DNR's Standard Survey on July 28, 2025 caught 3.93 walleye per gill net at Boy Lake. Length samples in the latest survey that recorded them ran 10–26 inches. DNR survey details →
Free interactive depth-contour map of Boy Lake, reaching a maximum surveyed depth of 45 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Boy Lake is a 3,308-acre mesotrophic lake in Cass County, Minnesota with a maximum depth of 45 feet. Overall water quality is improving over recent sampling years. The lake supports 20 documented fish species including black bullhead, black crappie, and bluegill. Public access is available. Compared to the 103 other monitored lakes in Cass County, Boy Lake ranks #51 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-07. Methodology: how these readings are compared.
Boy Lake covers about 3,300 acres in Cass County. Vrbo is where to look for cabins and lake homes around Boy Lake, and Booking.com and Expedia search hotels near the lake for your dates.
What Boy Lake is good for
From access and monitoring records, not editorial picks.
- Clear water10.5 ft of visibility
- Fishing20 species recorded
- Deep water45 ft surveyed max depth
- Big water3,308 acres
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. Check local advisories before you swim.
Whether Boy 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 Boy Lake
These are the measurements Minnesota PCA publishes for Boy Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Good clarity, visible to about 10.5 ft. Phosphorus 21 µg/L. Chlorophyll-a 6.3 µg/L. TSI 47.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 10.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 21µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 6.3µg/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. | 47 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Boy Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Boy Lake typically sits around 60°F at the surface in October. Summer average is about 66°F. Usually warmest in Jul (about 69°F) and coldest in May (about 56°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (56°F) to its warmest (69°F).
Typical surface water temperature by month, from 243 field readings (2011–2025) via the EPA Water Quality Portal. See the full Boy Lake water temperature breakdown →
Minnesota DNR's Standard Survey on July 28, 2025 caught 3.93 walleye per gill net at Boy Lake. Length samples in the latest survey that recorded them ran 10–26 inches.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Boy Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
11 surveys on file from MN DNR Fisheries. Most recent: 2025-07-28 (Standard Survey).
11 surveys on file · most recent 2025-07-28 (Standard Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Yellow Perch | 7.53 | 5–9 in 2025-07-28 | 0.16 lb |
| Bluegill | 5.58 | 1–9 in 2025-07-28 | 0.31 lb |
| Northern Pike | 5.38 | 10–30 in 2025-07-28 | 1.34 lb |
| Black Bullhead | 4.78 | 11–12 in 2021-08-02 | 0.75 lb |
| Pumpkinseed | 3.78 | 2–7 in 2025-07-28 | 0.2 lb |
| Walleye | 3.43 | 10–26 in 2025-07-28 | 2.6 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.
Yellow Perch
Bluegill
Northern Pike
Black Bullhead
From the 2025-07-28 survey
Boy Lake is a 3,466-acre lake with 2,007 littoral acres, 26 miles of shoreline and a maximum depth of 45 feet located north of Longville, MN. A DNR owned public access is located on the southwest shore. The DNR has classified Minnesota's lakes into 43 different classes based on physical, chemical and other…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Boy Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — BoyFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Boy (1566)Aquatic Plant Report · MN DNR LakeFinder
- —Public Water Access Sites — BoyPublic Water Access Sites · MN DNR LakeFinder
Lake Details
Max depth
45 ft
Surface area
3,308 acres
Shoreline
21.6 mi
Littoral zone
61%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
Lake Size & Watershed
Watershed (drainage) area
295 sq mi
HydroLAKES / HydroSHEDS
Elevation
1,286 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Stays via Stay22
Stays near Boy Lake
Compare lakeside cabins, hotels, and vacation rentals near Boy Lake in Cass 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.
Top-rated places to stay near Boy Lake
Prices for Oct 9–11, 4 adults. Change dates on the map below.
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Fish Species
Click a species to see every lake where it is documented.
Fishing Boy 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.
Water Quality Trend: Improving
Based on 6 years of monitoring (2020–2025).
Water clarity
Improving6 years
Phosphorus
Improving-0.81 µg/L/yr6 years
Chlorophyll-a
Improving-1.02 µg/L/yr6 years
Nearby Lakes in Cass County
Frequently asked questions about Boy Lake
Where is Boy Lake?
- Boy Lake is a lake in Cass County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of Boy Lake?
- Boy Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 10.5 ft visibility. Phosphorus: 21 µg/L. Chlorophyll-a (algae): 6.3 µg/L. Maximum depth: 45 ft. Surface area: 3307.75 acres.
Is Boy 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 Boy Lake?
- Boy Lake typically sits around 60°F at the surface in October, from 243 EPA Water Quality Portal field readings (2011–2025). That is a typical value for the month, not a live reading.
How deep is Boy Lake?
- Boy Lake has a maximum depth of 45 feet. The lake covers 3307.75 acres.
What fish are in Boy Lake?
- Fish species found in Boy Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, burbot, greater redhorse, hybrid sunfish, largemouth bass, muskellunge, northern pike, pumpkinseed, rock bass, shorthead redhorse, smallmouth bass, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. Boy Lake is located in Cass County, Minnesota.
What did the DNR fisheries survey find at Boy Lake?
- Minnesota DNR's Standard Survey on July 28, 2025 caught 3.93 walleye per gill net at Boy Lake. Length samples in the latest survey that recorded them ran 10–26 inches. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Boy Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
Can I fish at Boy Lake?
- Public access to Boy 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.
Explore Boy Lake across LakeQuality
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Where this data comes from
123 measurements from 4 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
MNPCA87 samples · 2020–2025 - Leech Lake Band of Ojibwe
LEECHLAK_WQX36 samples · 2024–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Nitrate-Nitrite Nitrogen by Colorimetry
Monitoring station identifiers (4)
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