Little Boy Lake
Little Boy Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 11 ft visibility. Phosphorus: 14 µg/L. Chlorophyll-a (algae): 5.1 µg/L. Maximum depth: 74 ft. Surface area: 1451.67 acres.
- Clarity
- 11 ft
- Typical in August
- 63°F
- Max depth
- 74 ft
- Area
- 1,452 acres
- Type
- Mesotrophic
- Trend
- → Stable
- Public access
- Yes
- Ice-out
- Apr 23
- Open water
- 222 days
Next lake in Cass County
Free interactive depth-contour map of Little Boy Lake, reaching a maximum surveyed depth of 70 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Little Boy Lake is a 1,452-acre mesotrophic lake in Cass County, Minnesota with a maximum depth of 74 feet. Water quality is graded A based on 2 sampling years through 2025. Phosphorus level is declining over recent sampling years. The lake supports 18 documented fish species including black bullhead, black crappie, and bluegill. Public access is available. Compared to the 103 other monitored lakes in Cass County, Little Boy Lake ranks #36 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-29. 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 11 ft. Phosphorus level: 14 µg/L. Chlorophyll-a: 5.1 µg/L. Trophic State Index: 44.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11 ft | Not graded |
| Phosphorus | 14 µg/L | Good |
| Chlorophyll-a (Algae) | 5.1 µg/L | Good |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Little Boy Lake
Compare lakeside cabins, hotels, and vacation rentals near Little 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
Little Boy Lake typically sits around 63°F at the surface in August. Summer average is about 66°F. Usually warmest in Jul (about 71°F) and coldest in May (about 57°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 170 field readings (2016–2025) via the EPA Water Quality Portal. See the full Little Boy Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 74 ft |
| Surface Area | 1,452 acres |
| Shoreline Length | 10 mi |
| Littoral Zone | 32% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Little Boy Lake
DNR Fisheries Survey Summary
19 surveys on file from MN DNR Fisheries. Most recent: 2024-07-29 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Yellow Perch | 18.68 | 0.14 lb |
| Walleye | 12.60 | 1.79 lb |
| Bluegill | 8.06 | 0.18 lb |
| BCS | 6.54 | — |
| MTS | 6.07 | — |
| BKF | 5.94 | — |
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
Walleye
Bluegill
From the 2024-07-29 survey
Temperature and dissolved oxygen profiles were collected in the deepest basins in Little Boy Lake on July 30, 2024 , 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 lake. Cisco…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Little Boy Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — Little BoyFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Little Boy (1529)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — Little BoyFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — Little BoyPublic 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 | +0.01 m/yr | 6 |
| Phosphorus | ↓ Declining | +0.63 µg/L/yr | 6 |
| Chlorophyll-a | ↑ Improving | -0.25 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (42 observations).
Estimated open water season: 222 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2012-03-27 (2012) | 2013-05-13 (2013) |
| Ice-In | 2018-11-20 (2018) | 2015-12-28 (2015) |
Most recent ice-out: 2023-05-03
EPA Impairment Status
Little Boy 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 MN11-0167-00 · Official waterbody report
County Ranking
Ranked #36 of 104 lakes in Cass County
Nearby Lakes in Cass County
Frequently asked questions about Little Boy Lake
What is the water quality grade for Little Boy Lake?
- Little Boy Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 11 ft visibility. Phosphorus: 14 µg/L. Chlorophyll-a (algae): 5.1 µg/L. Maximum depth: 74 ft. Surface area: 1451.67 acres.
Is Little Boy Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Little Boy Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 5.1 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Little Boy Lake?
- Little Boy Lake typically sits around 63°F at the surface in August, from 170 EPA Water Quality Portal field readings (2016–2025). That is a typical value for the month, not a live reading.
How deep is Little Boy Lake?
- Little Boy Lake has a maximum depth of 74 feet. The lake covers 1451.67 acres.
What fish are in Little Boy Lake?
- Fish species found in Little Boy Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, cisco species, hybrid sunfish, largemouth bass, muskellunge, northern pike, pumpkinseed, rock bass, smallmouth bass, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. Little Boy Lake is located in Cass County, Minnesota.
When does Little Boy Lake thaw?
- Little Boy Lake typically has ice-out around Apr 23. Ice typically forms around Dec 1. The open water season is approximately 222 days.
Explore Little Boy Lake across LakeGrade
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Species activity outlook by water temperature and season
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Moderate nutrients, good water quality
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Where this data comes from
188 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
MNPCA188 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
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
Ice data from Minnesota DNR Climate