Island Lake
Island Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 8.2 ft visibility. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 3.9 µg/L.
- Clarity
- 8.2 ft
- Typical in August
- 71°F
- Mean depth
- ~10 ft est.
- Type
- Mesotrophic
- Trend
- ↓ Declining
- Public access
- No
Next lake in Cass County
Island Lake is a mesotrophic lake in Cass County, Minnesota with an estimated average depth of about 10 feet. Water quality is graded A based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. Limited fish-species data available. No public access — the lake is private or restricted. Compared to the 103 other monitored lakes in Cass County, Island Lake ranks #16 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-12. Grade methodology: LakeGrade methodology.
Watch Island Lake water quality
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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)
Moderate clarity, visible to about 8.2 ft. Phosphorus level: 20 µg/L. Chlorophyll-a: 3.9 µg/L. Trophic State Index: 46.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 8.2 ft | Not graded |
| Phosphorus | 20 µg/L | Good |
| Chlorophyll-a (Algae) | 3.9 µg/L | Good |
| Trophic State Index (TSI) | 46 | 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 71°F at the surface in August. Summer average is about 69°F. Usually warmest in Aug (about 71°F) and coldest in May (about 58°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 45 field readings (2023–2024) via the EPA Water Quality Portal.
Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~10 ft est. |
| Public Access | No |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Minnesota has not published bathymetry for Island Lake.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Fishing Island Lake
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Island Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Aquatic Plant Report — Island (1475)Aquatic Plant Report · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.58 m/yr | 2 |
| Phosphorus | ↓ Declining | +8.5 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -0.4 µg/L/yr | 2 |
County Ranking
Ranked #16 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: 8.2 ft visibility. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 3.9 µg/L.
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 3.9 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Island Lake?
- Island Lake typically sits around 71°F at the surface in August, from 45 EPA Water Quality Portal field readings (2023–2024). That is a typical value for the month, not a live reading.
How deep is Island Lake?
- No published bathymetric survey covers Island Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 10 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
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Where this data comes from
27 measurements from 1 monitoring station, 2023–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA27 samples · 2023–2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by 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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder