Long Lake
Long Lake in Watonwan County, Minnesota has a water quality grade of D (Nutrient-rich). Water clarity: 2.5 ft visibility. Phosphorus: 58 µg/L. Chlorophyll-a (algae): 14.6 µg/L. Maximum depth: 13 ft. Surface area: 263.29 acres.
- Clarity
- 2.5 ft
- Typical in August
- 79°F
- Max depth
- 13 ft
- Area
- 263 acres
- Type
- Eutrophic
- Trend
- → Stable
- Public access
- Yes
Grade D measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Long Lake →
Next lake in Watonwan County
Long Lake is a 263-acre productive, nutrient-rich eutrophic lake in Watonwan County, Minnesota with a maximum depth of 13 feet. Water quality is graded D based on 2 sampling years through 2025. Water clarity is declining over recent sampling years. The lake supports 13 documented fish species including bigmouth buffalo, black bullhead, and black crappie. Public access is available with 1 public boat landing. Compared to the 3 other monitored lakes in Watonwan County, Long Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-09-03. Grade methodology: LakeGrade methodology.
Watch Long Lake water quality
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Swimming Safety
Grade onlyElevated nutrients
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.
Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum
Water Quality Grade: D (Nutrient-rich)
Very murky, less than 2.5 ft of visibility. Phosphorus level: 58 µg/L. Chlorophyll-a: 14.6 µg/L. Trophic State Index: 61.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.5 ft | Not graded |
| Phosphorus | 58 µg/L | Poor |
| Chlorophyll-a (Algae) | 14.6 µg/L | Fair |
| Trophic State Index (TSI) | 61 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Long Lake
Compare lakeside cabins, hotels, and vacation rentals near Long Lake in Watonwan 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Long Lake are listed below.
Top-rated places to stay near Long Lake
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Long Lake typically sits around 79°F at the surface in August. Summer average is about 76°F. Usually warmest in Jul (about 79°F) and coldest in Jun (about 71°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 42 field readings (2024–2025) 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 moderate (21,281 cells/mL) on January 25, 2025.
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 | 13 ft |
| Surface Area | 263 acres |
| Shoreline Length | 4.7 mi |
| Littoral Zone | 100% |
| 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
14 surveys on file from MN DNR Fisheries. Most recent: 2023-09-18 (Targeted Survey).
Top Species by Catch Rate
| Species | Avg CPUE | Avg Weight |
|---|---|---|
| Black Bullhead | 27.93 | 0.48 lb |
| Bluegill | 24.99 | 0.2 lb |
| Walleye | 22.05 | 2.86 lb |
| Black Crappie | 19.69 | 0.17 lb |
| Yellow Perch | 16.19 | 0.14 lb |
| CRP | 11.36 | 2.29 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.
Black Bullhead
Bluegill
Walleye
Black Crappie
From the 2023-09-18 survey
Long Lake is a 264-acre, class 43 lake, located in Watonwan County, approximately 5.5 miles south of the City of St. James. The lake has a maximum depth of 13.0 feet and has a watershed-to-lake-ratio of 6 to 1. The lakes watershed is highly agricultural and much of Long Lake's shoreline has been altered by residential…
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: → Stable
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.044 m/yr | 3 |
| Phosphorus | ↑ Improving | -11.18 µg/L/yr | 3 |
| Chlorophyll-a | → Stable | -0.2 µg/L/yr | 2 |
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 MN83-0040-00 · Official waterbody report
County Ranking
Ranked #3 of 4 lakes in Watonwan County
Nearby Lakes With Higher Grades
Long Lake holds Grade D. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Watonwan County
Frequently asked questions about Long Lake
What is the water quality grade for Long Lake?
- Long Lake in Watonwan County, Minnesota has a water quality grade of D (Nutrient-rich). Water clarity: 2.5 ft visibility. Phosphorus: 58 µg/L. Chlorophyll-a (algae): 14.6 µg/L. Maximum depth: 13 ft. Surface area: 263.29 acres.
Is Long Lake safe to swim in?
- Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Long Lake has a water quality grade of D (Nutrient-rich). Algae concentration (chlorophyll-a) is 14.6 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Long Lake?
- Long Lake typically sits around 79°F at the surface in August, from 42 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Long Lake?
- Long Lake has a maximum depth of 13 feet. The lake covers 263.29 acres.
What fish are in Long Lake?
- Fish species found in Long Lake include bigmouth buffalo, black bullhead, black crappie, bluegill, channel catfish, common carp, freshwater drum, hybrid sunfish, largemouth bass, northern pike, walleye, yellow bullhead, yellow perch. Long Lake is located in Watonwan County, Minnesota.
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 moderate (21,281 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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Fish species and best lakes in Watonwan County
Species activity outlook by water temperature and season
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High nutrients, frequent algae, reduced clarity
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State Parks Near Long Lake
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Where this data comes from
29 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
MNPCA29 samples · 2020–2025
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by 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