Long Lake
Long Lake in Cass County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 21.5 ft visibility. Maximum depth: 115 ft. Surface area: 1007.4 acres.
- Clarity
- 21.5 ft
- Typical in August
- 53°F
- Max depth
- 115 ft
- Area
- 1,007 acres
- Trend
- ↓ Declining
- Public access
- Yes
- Ice-out
- Apr 21
- Open water
- 221 days
Next lake in Cass County
Free interactive depth-contour map of Long Lake, reaching a maximum surveyed depth of 110 ft. Toggle Depth contours to overlay the bathymetric survey lines. Contour data from Minnesota DNR.
Why Long Lake has no grade
We grade a lake only when its monitoring record clears the evidence bar: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Long Lake, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). Sampling here has recorded water clarity, but not phosphorus and algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by MPCA and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Long Lake is a 1,007-acre lake in Cass County, Minnesota with a maximum depth of 115 feet. Overall water quality is declining over recent sampling years. The lake supports 14 documented fish species including black bullhead, black crappie, and bluegill. Public access is available.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2022-07-06. Grade methodology: LakeGrade methodology.
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Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Long Lake
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Crystal clear, you can see 21.5 ft down. Trophic State Index: 33.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 21.5 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 33 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Long Lake
Compare lakeside cabins, hotels, and vacation rentals near Long 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.
Top-rated places to stay near Long Lake
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Long Lake typically sits around 53°F at the surface in August. Summer average is about 53°F. Usually warmest in Jun (about 54°F) and coldest in May (about 47°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 499 field readings (2011–2025) via the EPA Water Quality Portal. See the full Long Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 115 ft |
| Surface Area | 1,007 acres |
| Shoreline Length | 16 mi |
| Littoral Zone | 35% |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Long Lake
DNR Fisheries Survey Summary
13 surveys on file from MN DNR Fisheries. Most recent: 2025-08-11 (Standard Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluntnose Minnow | 40.95 | — |
| CNM | 28.21 | — |
| Bluegill | 18.55 | 0.11 lb |
| Largemouth Bass | 9.99 | 0.79 lb |
| Northern Pike | 5.02 | 1.37 lb |
| BNS | 4.27 | — |
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
Largemouth Bass
Northern Pike
From the 2025-08-11 survey
Long Lake (DOW# 11-0142; Lake Class 25) is a 1007-acre lake with 15.96 miles of shoreline and a maximum depth of 115 feet located near Longville, MN. A DNR owned public access is located on the northwest shore. The DNR has classified Minnesota's lakes into 43 different classes based on physical, chemical and other…
DNR Reports & Resources
Minnesota DNR LakeFinder publishes lake survey, fish stocking, water access, and aquatic plant data for Long Lake. 3 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Fisheries Lake Survey — LongFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — LongFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — LongPublic Water Access Sites · MN DNR LakeFinder
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.099 m/yr | 6 |
| Phosphorus | → Stable | -0.19 µg/L/yr | 6 |
| Chlorophyll-a | ↓ Declining | +0.21 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (84 observations).
Estimated open water season: 221 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2012-03-25 (2012) | 2013-05-11 (2013) |
| Ice-In | 1995-11-13 (1995) | 2015-12-27 (2015) |
Most recent ice-out: 2025-04-18
Graded lakes near Long Lake
Long Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Cass County
Frequently asked questions about Long Lake
What is the water quality grade for Long Lake?
- Long Lake in Cass County, Minnesota is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 21.5 ft visibility. Maximum depth: 115 ft. Surface area: 1007.4 acres.
Is Long Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Long Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
What is the water temperature of Long Lake?
- Long Lake typically sits around 53°F at the surface in August, from 499 EPA Water Quality Portal field readings (2011–2025). That is a typical value for the month, not a live reading.
How deep is Long Lake?
- Long Lake has a maximum depth of 115 feet. The lake covers 1007.4 acres.
What fish are in Long Lake?
- Fish species found in Long Lake include black bullhead, black crappie, bluegill, brown bullhead, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, rock bass, tullibee (cisco), walleye, yellow bullhead, yellow perch. Long Lake is located in Cass County, Minnesota.
When does Long Lake thaw?
- Long Lake typically has ice-out around Apr 21. Ice typically forms around Nov 28. The open water season is approximately 221 days.
Explore Long Lake across LakeGrade
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Where this data comes from
2 measurements from 1 monitoring station, 2021–2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North American Lake Management Society
NALMS2 samples · 2021–2022
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
Ice data from Minnesota DNR Climate