Island Lake
Island Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 15.5 ft visibility. Phosphorus: 21.5 µg/L. Chlorophyll-a (algae): 2.6 µg/L. Maximum depth: 45 ft. Surface area: 358.3 acres.
- Clarity
- 15.5 ft
- Typical in August
- 68°F
- Max depth
- 45 ft
- Area
- 358 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
- Ice-out
- Apr 15
- Open water
- 231 days
Next lake in Cass County
Island Lake is a 358-acre mesotrophic lake in Cass County, Minnesota with a maximum depth of 45 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 12 documented fish species including black crappie, bluegill, and bowfin (dogfish). Public access is available with 1 public boat landing. Compared to the 103 other monitored lakes in Cass County, Island Lake ranks #14 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-22. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLimited data
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 15.5 ft down. Phosphorus level: 21.5 µg/L. Chlorophyll-a: 2.6 µg/L. Trophic State Index: 42.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 15.5 ft | Not graded |
| Phosphorus | 21.5 µg/L | Good |
| Chlorophyll-a (Algae) | 2.6 µg/L | Good |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Island Lake
Compare lakeside cabins, hotels, and vacation rentals near Island 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
Island Lake typically sits around 68°F at the surface in August. Summer average is about 66°F. Usually warmest in Aug (about 68°F) and coldest in May (about 52°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 118 field readings (2010–2025) via the EPA Water Quality Portal. See the full Island Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Island Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (293,765 cells/mL) on May 9, 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 | 45 ft |
| Surface Area | 358 acres |
| Shoreline Length | 5.8 mi |
| Littoral Zone | 17% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Island LakePublic
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Island Lake
DNR Fisheries Survey Summary
6 surveys on file from MN DNR Fisheries. Most recent: 2022-08-01 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 9.23 | 0.16 lb |
| Yellow Bass | 3.87 | 0.56 lb |
| Northern Pike | 3.87 | 1.24 lb |
| Largemouth Bass | 3.42 | 1.2 lb |
| Black Crappie | 3.04 | 0.45 lb |
| Rock Bass | 1.12 | 0.49 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
Yellow Bass
Northern Pike
Largemouth Bass
From the 2022-08-01 survey
Island Lake is a 358-acre lake with 5.8 miles of shoreline and a maximum depth of 45 feet located southeast of Longville, MN. A county owned public access is located on the west shore. The DNR has classified Minnesota's lakes into 43 different classes based on physical, chemical and other characteristics. Island Lake…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Island Lake. 4 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — IslandFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Island (1570)Aquatic Plant Report · MN DNR LakeFinder
- —Fish Stocking History — IslandFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — IslandPublic 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 | +0.215 m/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (8 observations).
Estimated open water season: 231 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2005-04-10 (2005) | 2022-05-06 (2022) |
| Ice-In | 2021-11-26 (2021) | 2024-12-04 (2024) |
Most recent ice-out: 2022-05-06
EPA Impairment Status
Island 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 MN11-0114-00 · Official waterbody report · Matched by proximity (1.73 km)
County Ranking
Ranked #14 of 104 lakes in Cass County
Nearby Lakes in Cass County
Frequently asked questions about Island Lake
What is the water quality grade for Island Lake?
- Island Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 15.5 ft visibility. Phosphorus: 21.5 µg/L. Chlorophyll-a (algae): 2.6 µg/L. Maximum depth: 45 ft. Surface area: 358.3 acres.
Is Island Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Island Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 2.6 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Island Lake?
- Island Lake typically sits around 68°F at the surface in August, from 118 EPA Water Quality Portal field readings (2010–2025). That is a typical value for the month, not a live reading.
How deep is Island Lake?
- Island Lake has a maximum depth of 45 feet. The lake covers 358.3 acres.
What fish are in Island Lake?
- Fish species found in Island Lake include black crappie, bluegill, bowfin (dogfish), brown bullhead, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, rock bass, walleye, yellow bullhead. Island Lake is located in Cass County, Minnesota.
When does Island Lake thaw?
- Island Lake typically has ice-out around Apr 15. Ice typically forms around Dec 2. The open water season is approximately 231 days.
Does Island Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Island Lake (clouds, ice, or an off-season gap). The most recent reading was high (293,765 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Are there boat ramps on Island Lake?
- Island Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Island Lake. Public access is listed as yes.
Explore Island Lake across LakeGrade
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Moderate nutrients, good water quality
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Where this data comes from
101 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
MNPCA101 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by 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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate