Long Lake
Long Lake in Otter Tail County, Minnesota has a water quality grade of A (Excellent). Water clarity: 11.6 ft visibility. Phosphorus: 17 µg/L. Chlorophyll-a (algae): 3.9 µg/L. Maximum depth: 73 ft. Surface area: 766.84 acres.
- Clarity
- 11.6 ft
- Typical in August
- 74°F
- Max depth
- 73 ft
- Area
- 767 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
- Ice-out
- Apr 12
- Open water
- 236 days
Next lake in Otter Tail County
Long Lake is a 767-acre mesotrophic lake in Otter Tail County, Minnesota with a maximum depth of 73 feet. Water quality is graded A based on 2 sampling years through 2025. Overall water quality is improving over recent sampling years. The lake supports 17 documented fish species including bigmouth buffalo, black bullhead, and black crappie. Public access is available with 1 public boat landing. Compared to the 65 other monitored lakes in Otter Tail County, Long Lake ranks #6 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-22. Grade methodology: LakeGrade methodology.
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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)
Good clarity, visible to about 11.6 ft. Phosphorus level: 17 µg/L. Chlorophyll-a: 3.9 µg/L. Trophic State Index: 44.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11.6 ft | Not graded |
| Phosphorus | 17 µg/L | Good |
| Chlorophyll-a (Algae) | 3.9 µg/L | Good |
| Trophic State Index (TSI) | 44 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Long Lake
Compare lakeside cabins, hotels, and vacation rentals near Long Lake in Otter Tail 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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Water Temperature
Long Lake typically sits around 74°F at the surface in August. Summer average is about 71°F. Usually warmest in Aug (about 74°F) and coldest in May (about 54°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 40 field readings (2010–2023) via the EPA Water Quality Portal. See the full Long Lake water temperature breakdown →
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 (183,654 cells/mL) on May 23, 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 | 73 ft |
| Surface Area | 767 acres |
| Shoreline Length | 7.5 mi |
| Littoral Zone | 40% |
| 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
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
DNR Fisheries Survey Summary
9 surveys on file from MN DNR Fisheries. Most recent: 2023-07-24 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Bluegill | 24.45 | 0.15 lb |
| Largemouth Bass | 12.11 | 0.84 lb |
| Yellow Bass | 8.34 | 0.7 lb |
| Hybrid Sunfish | 5.61 | 0.26 lb |
| Northern Pike | 5.58 | 1.48 lb |
| Black Crappie | 5.37 | 0.45 lb |
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
Yellow Bass
Hybrid Sunfish
From the 2023-07-24 survey
Long Lake is a 756-acre mesotrophic (moderately fertile) lake located in west-central Otter Tail County approximately nine miles north of Fergus Falls, MN. Long Lake is located within the Otter Tail River Watershed. An inlet is located along the east shoreline and an outlet dam is located along the northwest…
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 | ↑ Improving | +0.52 m/yr | 6 |
| Phosphorus | → Stable | -0.31 µg/L/yr | 6 |
| Chlorophyll-a | ↑ Improving | -0.46 µg/L/yr | 6 |
Ice Season
Historical ice data from Minnesota DNR (10 observations).
Estimated open water season: 236 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2016-03-25 (2016) | 2018-04-29 (2018) |
| Ice-In | 2017-11-22 (2017) | 2016-12-09 (2016) |
Most recent ice-out: 2021-03-30
EPA Impairment Status
Long Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit MN56-0784-00 · Official waterbody report
County Ranking
Ranked #6 of 66 lakes in Otter Tail County
Nearby Lakes in Otter Tail County
Frequently asked questions about Long Lake
What is the water quality grade for Long Lake?
- Long Lake in Otter Tail County, Minnesota has a water quality grade of A (Excellent). Water clarity: 11.6 ft visibility. Phosphorus: 17 µg/L. Chlorophyll-a (algae): 3.9 µg/L. Maximum depth: 73 ft. Surface area: 766.84 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 3.9 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Long Lake?
- Long Lake typically sits around 74°F at the surface in August, from 40 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
How deep is Long Lake?
- Long Lake has a maximum depth of 73 feet. The lake covers 766.84 acres.
What fish are in Long Lake?
- Fish species found in Long Lake include bigmouth buffalo, black bullhead, black crappie, bluegill, bowfin (dogfish), brown bullhead, green sunfish, hybrid sunfish, largemouth bass, northern pike, pumpkinseed, rock bass, tullibee (cisco), walleye, white sucker, yellow bullhead, yellow perch. Long Lake is located in Otter Tail County, Minnesota.
When does Long Lake thaw?
- Long Lake typically has ice-out around Apr 12. Ice typically forms around Dec 4. The open water season is approximately 236 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 (183,654 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.
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Where this data comes from
89 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA89 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
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
Impairment status from EPA ATTAINS 303(d) database
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