Long Lake
Long Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Water clarity: 21.5 ft visibility. Phosphorus: 9 µg/L. Chlorophyll-a (algae): 3 µg/L. Maximum depth: 115 ft. Surface area: 1007.4 acres.
- Clarity
- 21.5 ft
- Max depth
- 115 ft
- Area
- 1,007 acres
- Type
- Oligotrophic
- Trend
- ↑ Improving
- Public access
- Yes
- Ice-out
- Apr 21
- Open water
- 221 days
Next lake in Cass County
Long Lake is a 1,007-acre cold, clear oligotrophic lake in Cass County, Minnesota with a maximum depth of 115 feet. Water quality is graded A based on 3 sampling years through 2025. Overall water quality is improving over recent sampling years. The lake supports 14 documented fish species including black bullhead, black crappie, and bluegill. Public access is available with 1 public boat landing. Compared to the 103 other monitored lakes in Cass County, Long Lake ranks #7 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-07. Grade methodology: LakeGrade methodology.
Watch Long 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)
Crystal clear, you can see 21.5 ft down. Phosphorus level: 9 µg/L. Chlorophyll-a: 3 µg/L. Trophic State Index: 37.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 21.5 ft | Not graded |
| Phosphorus | 9 µg/L | Good |
| Chlorophyll-a (Algae) | 3 µg/L | Good |
| Trophic State Index (TSI) | 37 | 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.
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Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Long Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (328,095 cells/mL) on May 26, 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 | 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).
Recreation & Access
- Long LakePublic
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: ↑ Improving
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.039 m/yr | 6 |
| Phosphorus | ↑ Improving | -0.21 µg/L/yr | 6 |
| Chlorophyll-a | → Stable | +0.07 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
County Ranking
Ranked #7 of 104 lakes in Cass County
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 has a water quality grade of A (Excellent). Water clarity: 21.5 ft visibility. Phosphorus: 9 µg/L. Chlorophyll-a (algae): 3 µg/L. Maximum depth: 115 ft. Surface area: 1007.4 acres.
Is Long Lake safe to swim in?
- Excellent for swimming, crystal clear water with minimal algae. Long Lake has a water quality grade of A (Excellent). Algae concentration (chlorophyll-a) is 3 µg/L. Always check local health department advisories before swimming.
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.
Does Long Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Long Lake (clouds, ice, or an off-season gap). The most recent reading was high (328,095 cells/mL). Blue-green algae can appear and clear within days, so check Minnesota's current advisory before swimming.
Are there boat ramps on Long Lake?
- Long Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Long Lake. Public access is listed as yes.
Explore Long Lake across LakeGrade
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Where this data comes from
281 measurements from 5 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
MNPCA246 samples · 2020–2025 - Leech Lake Band of Ojibwe
LEECHLAK_WQX35 samples · 2024–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Nitrate-Nitrite Nitrogen by Colorimetry
Monitoring station identifiers (5)
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
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate