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Little Boy Lake

Cass County, MinnesotaMesotrophic

On the LakeGrade rubric, Little Boy Lake pulls an A: clarity at 11.0 ft and 14 µg/L of phosphorus put it in the top bracket for Minnesota. The two scored sub-grades — clarity and phosphorus — track close together, so neither one is dragging the average down.

The lake sits in the mesotrophic zone — the band where most well-managed Minnesota lakes fall. At 74 ft of maximum depth, Little Boy Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. At 1,452 acres, Little Boy Lake is one of the larger lakes in Cass County, with 10.0 miles of shoreline supporting multiple distinct use patterns. Little Boy Lake sits at rank 68 of 132 in Cass County, in the lower half of the local distribution.

Little Boy Lake has no invasive species recorded in Minnesota state databases as of 2024, though prevention practices still apply at all access points. Little Boy Lake's fishery is anchored by muskellunge, with 18 documented species in total — a destination water for muskie anglers. Public access is available — the lake is on the Minnesota PCA public-access list. Ice-out has been recorded 23 times at Little Boy Lake, with a median around Apr 23. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.

Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-22. Grade methodology: LakeGrade methodology.

Reviewed by LakeQuality Editorial Team · Updated

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Swimming Safety

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. Trophic State Index: 42.

MetricValueGrade
Water Clarity (Secchi Depth)11 ftB
Phosphorus14 µg/LA
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)42Mesotrophic

Moderate nutrients, good water quality

Lake Details

CharacteristicValue
Maximum Depth74 ft
Surface Area1.5K acres
Shoreline Length10 mi
Littoral Zone32%
Public AccessYes

Fish Species

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

Click a species to see all Minnesota and Wisconsin lakes where it is found.

→ Best fishing times for Little Boy Lake (14-day solunar calendar)

→ Is it safe to eat fish from Little Boy Lake? (mercury & PFAS guide)

Little Boy Lake fishing regulations (limits, seasons, special rules)

Water Quality Trend: Stable

Based on 5 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Water Clarity Stable+0.061 m/yr5
Phosphorus Stable+0.05 µg/L/yr5
See year-by-year chart →

Ice Season

Historical ice data from Minnesota DNR (42 observations).

Typical Ice-Out
Apr 23
Typical Ice-In
Dec 1

Estimated open water season: 222 days

EarliestLatest
Ice-Out2012-03-27 (2012)2013-05-13 (2013)
Ice-In2018-11-20 (2018)2015-12-28 (2015)

Most recent ice-out: 2023-05-03

Location

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County Ranking

Ranked #68 of 132 lakes in Cass County

Nearby Lakes in Cass County

DNR Fisheries Survey Summary

19 surveys on file from MN DNR Fisheries. Most recent: 2024-07-29 (Targeted Survey).

Top Species by Catch Rate

SpeciesAvg CPUEAvg Weight
Yellow Perch18.680.14 lb
Walleye12.601.79 lb
Bluegill8.060.18 lb
BCS6.54
MTS6.07
BKF5.94

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

201 fish · 410 in · 2024-06-24
12362045678910

Walleye

194 fish · 525 in · 2024-06-24
58290trophy 24681012141618202224

Bluegill

300 fish · 18 in · 2024-06-24
16080012345678

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…

Source: MN DNR LakeFinder Fisheries Lake Survey

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.

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

Mercury

A Total Maximum Daily Load (TMDL) plan has been approved.

Source: EPA ATTAINS assessment unit MN11-0167-00 · Official waterbody report

Data Sources

Water quality data from the EPA Water Quality Portal

Impairment status from EPA ATTAINS 303(d) database

Grading methodology based on Metropolitan Council standards

Lake details from Minnesota DNR LakeFinder

Ice data from Minnesota DNR Climate

Most recent sample: 2024-09-22

Monitoring stations: 1