Long Lake
Cass County, Minnesota1,007 acresView mapDirections
Minnesota PCA publishes the water-quality measurements for Long Lake. Here is what has been measured.
- Oligotrophic
- 115 ft max depth
- Public access
Long Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. 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.
Minnesota DNR's Standard Survey on August 11, 2025 caught 1.83 walleye per gill net at Long Lake. DNR survey details →
Long Lake is a 1,007-acre cold, clear oligotrophic lake in Cass County, Minnesota with a maximum depth of 115 feet. 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. Methodology: how these readings are compared.
What Long Lake is good for
From access and monitoring records, not editorial picks.
- Clear water21.5 ft of visibility
- Boat launch1 documented ramp
- Fishing14 species recorded
- Ice seasonIce-out around Apr 21
- Deep water115 ft surveyed max depth
- Big water1,007 acres
Swimming conditions
Readings onlyLow algae
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Long 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 Long Lake
These are the measurements Minnesota PCA publishes for Long Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Crystal clear, you can see 21.5 ft down. Phosphorus 9 µg/L. Chlorophyll-a 3 µg/L. TSI 37.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 21.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 9µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 3µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 37 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Long Lake
Answers come straight from the public measurements and survey records on this page.
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 ↗
Minnesota DNR's Standard Survey on August 11, 2025 caught 1.83 walleye per gill net at Long Lake.
A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Long Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
DNR Fisheries Survey Summary
13 surveys on file from MN DNR Fisheries. Most recent: 2025-08-11 (Standard Survey).
13 surveys on file · most recent 2025-08-11 (Standard Survey)
| Species | Catch rate (CPUE) | Size | Avg weight |
|---|---|---|---|
| Bluntnose Minnow | 40.95 | ||
| Bluegill | 18.55 | 3–8 in 2025-08-11 | 0.11 lb |
| Largemouth Bass | 9.99 | 5–18 in 2025-08-11 | 0.79 lb |
| Northern Pike | 5.02 | 9–36 in 2025-08-11 | 1.37 lb |
CPUE = catch per unit effort, fish caught per net per set in a standardised survey. It measures abundance, not size, and is not a weekly bite report.
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
Lake Details
Max depth
115 ft
Surface area
1,007 acres
Shoreline
16 mi
Littoral zone
35%
Share shallower than 15 ft
Public access
Yes
Listed by Minnesota PCA
Recreation & Access
- Long LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
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Stays near Long Lake
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Fish Species
Click a species to see every lake where it is documented.
Fishing Long Lake
Water Quality Trend: Improving
Based on 6 years of monitoring (2020–2025).
Water clarity
Stable6 years
Phosphorus
Improving-0.21 µg/L/yr6 years
Chlorophyll-a
Stable+0.07 µg/L/yr6 years
Ice season
Typical ice-out
Apr 21
Earliest Mar 25, 2012 · Latest May 11, 2013
Typical ice-in
Nov 28
Earliest Nov 13, 1995 · Latest Dec 27, 2015
Most recent ice-out
Apr 18
2025
84 observations · Minnesota PCA ice records
Nearby Lakes in Cass County
Frequently asked questions about Long Lake
Where is Long Lake?
- Long 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 Long Lake?
- Long Lake in Cass County, Minnesota has water-quality measurements published by Minnesota PCA, shown here as reported. 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?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
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.
What did the DNR fisheries survey find at Long Lake?
- Minnesota DNR's Standard Survey on August 11, 2025 caught 1.83 walleye per gill net at Long Lake. A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Long Lake’s water-quality measurements separately, and the water-quality trend over 6 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
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.
Can I fish at Long Lake?
- Long Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. 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
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)
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 details from Minnesota DNR LakeFinder
Named boat-access points from the USGS National Boat Ramps inventory
Ice data from Minnesota DNR Climate