Girl Lake
Girl Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 17.6 ft visibility. Phosphorus: 12 µg/L. Chlorophyll-a (algae): 2.7 µg/L. Maximum depth: 81 ft. Surface area: 428.18 acres.
- Clarity
- 17.6 ft
- Typical in August
- 56°F
- Max depth
- 81 ft
- Area
- 428 acres
- Type
- Oligotrophic
- Trend
- ↑ Improving
- Public access
- Yes
Next lake in Cass County
Girl Lake is a 428-acre cold, clear oligotrophic lake in Cass County, Minnesota with a maximum depth of 81 feet. Water quality is graded A based on 2 sampling years through 2025. Overall water quality is improving over recent sampling years. The lake supports 18 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, Girl Lake ranks #11 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)
Crystal clear, you can see 17.6 ft down. Phosphorus level: 12 µg/L. Chlorophyll-a: 2.7 µg/L. Trophic State Index: 39.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 17.6 ft | Not graded |
| Phosphorus | 12 µg/L | Good |
| Chlorophyll-a (Algae) | 2.7 µg/L | Good |
| Trophic State Index (TSI) | 39 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Girl Lake
Compare lakeside cabins, hotels, and vacation rentals near Girl 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
Girl Lake typically sits around 56°F at the surface in August. Summer average is about 68°F. Usually warmest in Jul (about 78°F) and coldest in Aug (about 56°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 113 field readings (2011–2024) via the EPA Water Quality Portal. See the full Girl Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Girl Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (108,643 cells/mL) on April 25, 2026.
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 | 81 ft |
| Surface Area | 428 acres |
| Shoreline Length | 9.4 mi |
| Littoral Zone | 64% |
| Public Access | Yes |
Recreation & Access
- Girl LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Girl 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
12 surveys on file from MN DNR Fisheries. Most recent: 2024-09-16 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 15.76 | 0.14 lb |
| Bluntnose Minnow | 12.65 | — |
| BCS | 11.11 | — |
| CNM | 8.82 | — |
| LES | 5.46 | 0.02 lb |
| Northern Pike | 5.34 | 1.74 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.
Bluegill
LES
Northern Pike
From the 2024-09-16 survey
Girl Lake is a 428-acre lake with 9.4 miles of shoreline and a maximum depth of 81 feet located in Longville, MN. A city owned public access is located on the east shore. The MNDNR has classified Minnesota's lakes into 43 different classes based on physical, chemical, and other characteristics. Moccasin Lake is in…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Girl Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — GirlFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Girl (1581)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — GirlFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — GirlPublic 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 | +0.197 m/yr | 6 |
| Phosphorus | → Stable | -0.23 µg/L/yr | 6 |
| Chlorophyll-a | ↑ Improving | -0.27 µg/L/yr | 6 |
EPA Impairment Status
Girl 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 MN11-0174-00 · Official waterbody report
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Girl Lake under Clean Water Act (NPDES) discharge permits.
- LongvilleLongville · 0.7 mi away · NPDES MN0046655
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
County Ranking
Ranked #11 of 104 lakes in Cass County
Nearby Lakes in Cass County
Frequently asked questions about Girl Lake
What is the water quality grade for Girl Lake?
- Girl Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 17.6 ft visibility. Phosphorus: 12 µg/L. Chlorophyll-a (algae): 2.7 µg/L. Maximum depth: 81 ft. Surface area: 428.18 acres.
Is Girl Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Girl Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 2.7 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Girl Lake?
- Girl Lake typically sits around 56°F at the surface in August, from 113 EPA Water Quality Portal field readings (2011–2024). That is a typical value for the month, not a live reading.
How deep is Girl Lake?
- Girl Lake has a maximum depth of 81 feet. The lake covers 428.18 acres.
What fish are in Girl Lake?
- Fish species found in Girl Lake include black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, green sunfish, hybrid sunfish, largemouth bass, muskellunge, northern pike, pumpkinseed, rock bass, smallmouth bass, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. Girl Lake is located in Cass County, Minnesota.
Does Girl Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Girl Lake (clouds, ice, or an off-season gap). The most recent reading was high (108,643 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Are there boat ramps on Girl Lake?
- Girl Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Girl Lake. Public access is listed as yes.
Explore Girl Lake across LakeGrade
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Where this data comes from
109 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
MNPCA109 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 (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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory