L Thunder Lake
Cass County, MinnesotaView mapDirections
Minnesota PCA publishes the water-quality measurements for L Thunder Lake. Here is what has been measured.
- 82 ft max depth
- Public access
- Limited data
L Thunder Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 14 ft visibility.
L Thunder Lake is a lake in Cass County, Minnesota with an estimated average depth of about 82 feet. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-09-02. Methodology: how these readings are compared.
What L Thunder Lake is good for
From access and monitoring records, not editorial picks.
- Clear water14 ft of visibility
- Ice seasonIce-out around Apr 18
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether L Thunder Lake is safe to swim in today is a call for the Minnesota Pollution Control Agency and the Minnesota DNR and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for L Thunder Lake
These are the measurements Minnesota PCA publishes for L Thunder Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Good clarity, visible to about 14 ft. TSI 39.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 14ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | No reading The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. | |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 39 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about L Thunder Lake
Answers come straight from the public measurements and survey records on this page.
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for L Thunder Lake. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Public Water Access Sites — Little Thunder (West Bay)Public Water Access Sites · MN DNR LakeFinder
Lake Details
Max depth
~82 ft est.
Public access
Yes
Listed by Minnesota PCA
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Minnesota has not published bathymetry for L Thunder Lake.
Lake Size & Watershed
Watershed (drainage) area
14 sq mi
HydroLAKES / HydroSHEDS
Surface area
225 acres
HydroLAKES / HydroSHEDS
Shoreline
5.4 mi
HydroLAKES / HydroSHEDS
Elevation
1,306 ft
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.
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Stays near L Thunder Lake
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Fishing L Thunder Lake
Water Quality Trend: Worsening
Based on 5 years of monitoring (2020–2024).
Water clarity
Worsening5 years
Ice season
Typical ice-out
Apr 18
Earliest Mar 17, 2024 · Latest May 1, 2018
Most recent ice-out
Mar 17
2024
8 observations · Minnesota PCA ice records
Nearby Lakes in Cass County
Frequently asked questions about L Thunder Lake
Where is L Thunder Lake?
- L Thunder Lake is a lake in Cass County, Minnesota. Its water-quality measurements are published by Minnesota PCA and shown on this page as reported.
What is the water quality of L Thunder Lake?
- L Thunder Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. Water clarity: 14 ft visibility.
Is L Thunder Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
How deep is L Thunder Lake?
- No published bathymetric survey covers L Thunder Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 82 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
When does L Thunder Lake thaw?
- L Thunder Lake typically has ice-out around Apr 18.
Can I fish at L Thunder Lake?
- Public access to L Thunder Lake is listed as yes on the lake record. Seasons, size and bag limits, and whether you need a license are set by Minnesota's fish and wildlife agency, so check its current regulations before you go.
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Where this data comes from
29 measurements from 1 monitoring station, 2020–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA29 samples · 2020–2024
Analytical methods
- Field measurement/observation, generic method
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Lake size & watershed from HydroLAKES (HydroSHEDS)
Lake details from Minnesota DNR LakeFinder
Ice data from Minnesota DNR Climate