Long Lake
Long Lake in Florence County, Wisconsin has a water quality grade of C (Fair). Water clarity: 7.9 ft visibility. Phosphorus: 25.2 µg/L. Maximum depth: 21 ft. Surface area: 353 acres.
- Clarity
- 7.9 ft
- Typical in August
- 67°F
- Max depth
- 21 ft
- Area
- 353 acres
- Type
- Mesotrophic
- Trend
- → Stable
- Public access
- Yes
Next lake in Florence County
Long Lake is a 353-acre mesotrophic lake in Florence County, Wisconsin with a maximum depth of 21 feet. Water quality is graded C based on 1 sampling years through 2025. Water clarity is improving over recent sampling years. The lake supports 3 documented fish species including Panfish, Largemouth Bass, and Northern Pike. Public access is available with 1 public boat landing. Compared to the 11 other monitored lakes in Florence County, Long Lake ranks #12 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-09-18. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyModerate
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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Moderate clarity, visible to about 7.9 ft. Phosphorus level: 25.2 µg/L. Trophic State Index: 49.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 7.9 ft | Not graded |
| Phosphorus | 25.2 µg/L | Fair |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 49 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Long Lake
Compare lakeside cabins, hotels, and vacation rentals near Long Lake in Florence County, Wisconsin — 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.
Top-rated places to stay near Long Lake
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Water Temperature
Long Lake typically sits around 67°F at the surface in August. Summer average is about 70°F. Usually warmest in Jul (about 73°F) and coldest in Feb (about 41°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 14 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 high (691,831 cells/mL) on June 27, 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 | 21 ft |
| Surface Area | 353 acres |
| 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.
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 2007. 1 station on file (most recent sample 2025).
Fish Species (DNR-rated)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Long Lake covering fish populations, stocking, water quality, and management. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- 2023Long Lake comprehensive survey, 2023Comprehensive Survey · WI DNR · 2023 (PDF)
Water Quality Trend: → Stable
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.572 m/yr | 4 |
| Phosphorus | ↓ Declining | +0.91 µg/L/yr | 4 |
County Ranking
Ranked #12 of 12 lakes in Florence County
Nearby Lakes With Higher Grades
Long Lake holds Grade C. 3 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Florence County
Frequently asked questions about Long Lake
What is the water quality grade for Long Lake?
- Long Lake in Florence County, Wisconsin has a water quality grade of C (Fair). Water clarity: 7.9 ft visibility. Phosphorus: 25.2 µg/L. Maximum depth: 21 ft. Surface area: 353 acres.
Is Long Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Long Lake has a water quality grade of C (Fair). Always check local health department advisories before swimming.
What is the water temperature of Long Lake?
- Long Lake typically sits around 67°F at the surface in August, from 14 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 21 feet. The lake covers 353 acres.
What fish are in Long Lake?
- Fish species found in Long Lake include Panfish, Largemouth Bass, Northern Pike. Long Lake is located in Florence County, Wisconsin.
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 (691,831 cells/mL). Blue-green algae can appear and clear within days, so check Wisconsin'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
32 measurements from 1 monitoring station, 2022–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX32 samples · 2022–2025
Analytical methods
- Phosphorus by Colorimetry
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Fish and recreation data from Wisconsin DNR Lakes
Named boat-access points from the USGS National Boat Ramps inventory