Sylvan Lake
Sylvan Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 19.5 ft visibility. Phosphorus: 7 µg/L. Chlorophyll-a (algae): 2.1 µg/L. Surface area: 1280 acres.
- Clarity
- 19.5 ft
- Mean depth
- ~25 ft est.
- Area
- 1,280 acres
- Type
- Oligotrophic
- Trend
- ↓ Declining
- Public access
- No
Next lake in Cass County
Free interactive depth-contour map of Sylvan Lake, reaching a maximum surveyed depth of 50 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Sylvan Lake is a 1,280-acre cold, clear oligotrophic lake in Cass County, Minnesota with an estimated average depth of about 25 feet. Water quality is graded A based on 2 sampling years through 2025. 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, Sylvan Lake ranks #46 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-08-17. 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 19.5 ft down. Phosphorus level: 7 µg/L. Chlorophyll-a: 2.1 µg/L. Trophic State Index: 35.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 19.5 ft | Not graded |
| Phosphorus | 7 µg/L | Good |
| Chlorophyll-a (Algae) | 2.1 µg/L | Good |
| Trophic State Index (TSI) | 35 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Sylvan Lake
Compare lakeside cabins, hotels, and vacation rentals near Sylvan 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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Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~25 ft est. |
| Surface Area | 1,280 acres |
| Public Access | No |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Minnesota has not published bathymetry for Sylvan 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 Sylvan 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.
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.139 m/yr | 6 |
Reservoir Info (USACE NID)
Sylvan Lake is a man-made reservoir impounded by the Sylvan (completed 1913), built primarily for hydroelectric on the Crow Wing; gravity-type dam, 35 ft tall and 1,154 ft long.
- Surface area
- 1,280 ac
- Normal storage
- 9,216 ac-ft
- Drainage area
- 3,575 sq mi
- Hazard class
- High
- Owner
- Allete, Inc.
All listed purposes: Hydroelectric;Recreation.
Source: USACE National Inventory of Dams, NID ID MN00601 · Operator website
EPA Impairment Status
Sylvan 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 MN11-0304-01 · Official waterbody report · Matched by proximity (0.87 km)
County Ranking
Ranked #46 of 104 lakes in Cass County
Nearby Lakes in Cass County
Frequently asked questions about Sylvan Lake
What is the water quality grade for Sylvan Lake?
- Sylvan Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 19.5 ft visibility. Phosphorus: 7 µg/L. Chlorophyll-a (algae): 2.1 µg/L. Surface area: 1280 acres.
Is Sylvan Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Sylvan Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 2.1 µg/L. Always check local health department advisories before swimming.
How deep is Sylvan Lake?
- No published bathymetric survey covers Sylvan Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 25 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 1280 acres.
Explore Sylvan Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
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Low nutrients, clear water, excellent for swimming
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Where this data comes from
71 measurements from 3 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
MNPCA71 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (3)
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