Long Lake
Long Lake in Dakota County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 1.6 ft visibility. Phosphorus: 110 µg/L. Chlorophyll-a (algae): 81.5 µg/L.
- Clarity
- 1.6 ft
- Typical in August
- 76°F
- Max depth
- ~24 ft est.
- Type
- Hypereutrophic
- Public access
- No
Grade F measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Long Lake →
Next lake in Dakota County
Long Lake is a highly nutrient-loaded hypereutrophic lake in Dakota County, Minnesota with an estimated average depth of about 24 feet. Water quality is graded F based on 2 sampling years through 2024. Limited fish-species data available. No public access — the lake is private or restricted. Compared to the 44 other monitored lakes in Dakota County, Long Lake ranks #33 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2024-10-17. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyLimited data
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.
Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom
Water Quality Grade: F (Algae-prone)
Very murky, less than 1.6 ft of visibility. Phosphorus level: 110 µg/L. Chlorophyll-a: 81.5 µg/L. Trophic State Index: 72.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | Not graded |
| Phosphorus | 110 µg/L | Poor |
| Chlorophyll-a (Algae) | 81.5 µg/L | Poor |
| Trophic State Index (TSI) | 72 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Long Lake
Compare lakeside cabins, hotels, and vacation rentals near Long Lake in Dakota 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
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Planning a whole trip? See where to stay at Minnesota’s top lakes →
Water Temperature
Long Lake typically sits around 76°F at the surface in August. Summer average is about 77°F. Usually warmest in Jul (about 83°F) and coldest in Apr (about 51°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 42 field readings (2010–2024) via the EPA Water Quality Portal. See the full Long Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~24 ft est. |
| Average Depth | ~9 ft est. |
| Public Access | No |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Minnesota has not published bathymetry for Long Lake.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Fishing Long Lake
EPA Impairment Status
Long Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit MN19-0022-00 · Official waterbody report
County Ranking
Ranked #33 of 45 lakes in Dakota County
Nearby Lakes With Higher Grades
Long Lake holds Grade F. 3 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
Nearby Lakes in Dakota County
Frequently asked questions about Long Lake
What is the water quality grade for Long Lake?
- Long Lake in Dakota County, Minnesota has a water quality grade of F (Algae-prone). Water clarity: 1.6 ft visibility. Phosphorus: 110 µg/L. Chlorophyll-a (algae): 81.5 µg/L.
Is Long Lake safe to swim in?
- Algae and nutrients are often high — check current advisories before swimming. Skip the water if you see scum or a paint-like bloom. Long Lake has a water quality grade of F (Algae-prone). Algae concentration (chlorophyll-a) is 81.5 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Long Lake?
- Long Lake typically sits around 76°F at the surface in August, from 42 EPA Water Quality Portal field readings (2010–2024). That is a typical value for the month, not a live reading.
How deep is Long Lake?
- No published bathymetric survey covers Long Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 24 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Long Lake across LakeGrade
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Where this data comes from
44 measurements from 1 monitoring station, 2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Minnesota Pollution Control Agency - Ambient Surface Water
MNPCA44 samples · 2024
Analytical methods
- Field measurement/observation, generic method
- Phosphorus by Colorimetry
- Analysis of Chlorophyll in Periphyton and Plankton
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