Boy Lake
Boy Lake in Cass County, Minnesota has a water quality grade of A (Excellent). 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.
- Clarity
- 10.5 ft
- Typical in August
- 67°F
- Max depth
- 45 ft
- Area
- 3,308 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
Next lake in Cass County
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. Water quality is graded A based on 3 sampling years through 2025. 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 with 1 public boat landing. 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. 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)
Good clarity, visible to about 10.5 ft. Phosphorus level: 21 µg/L. Chlorophyll-a: 6.3 µg/L. Trophic State Index: 47.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 10.5 ft | Not graded |
| Phosphorus | 21 µg/L | Good |
| Chlorophyll-a (Algae) | 6.3 µg/L | Good |
| Trophic State Index (TSI) | 47 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay 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.
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Water Temperature
Boy Lake typically sits around 67°F at the surface in August. 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.
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 →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 45 ft |
| Surface Area | 3,308 acres |
| Shoreline Length | 21.6 mi |
| Littoral Zone | 61% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Boy LakePublic
Fish Species
Click a species to see every graded 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.
DNR Fisheries Survey Summary
11 surveys on file from MN DNR Fisheries. Most recent: 2025-07-28 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Yellow Perch | 7.53 | 0.16 lb |
| Bluegill | 5.58 | 0.31 lb |
| Northern Pike | 5.38 | 1.34 lb |
| Black Bullhead | 4.78 | 0.75 lb |
| Pumpkinseed | 3.78 | 0.2 lb |
| Walleye | 3.43 | 2.6 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.
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
Water Quality Trend: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.16 m/yr | 6 |
| Phosphorus | ↑ Improving | -0.81 µg/L/yr | 6 |
| Chlorophyll-a | ↑ Improving | -1.02 µg/L/yr | 6 |
EPA Impairment Status
Boy 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 MN11-0143-00 · Official waterbody report
County Ranking
Ranked #51 of 104 lakes in Cass County
Nearby Lakes in Cass County
Frequently asked questions about Boy Lake
What is the water quality grade for Boy Lake?
- Boy Lake in Cass County, Minnesota has a water quality grade of A (Excellent). 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?
- Excellent for swimming, crystal clear water with minimal algae. Boy Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 6.3 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Boy Lake?
- Boy Lake typically sits around 67°F at the surface in August, 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.
Are there boat ramps on Boy Lake?
- Boy Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Boy Lake. Public access is listed as yes.
Explore Boy Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
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Fish species and best lakes in Cass County
Species activity outlook by water temperature and season
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Where to stay at Minnesota's top lakes, each with its grade
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Moderate nutrients, good water quality
Minnesota's cleanest and most-polluted lakes, ranked
More Minnesota Lake Rankings
State Parks Near Boy Lake
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Mesotrophic Lakes in Minnesota
Compare Boy Lake With Nearby Lakes
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)
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