Sea Lion Lake
Sea Lion Lake in Florence County, Wisconsin has a water quality grade of B (Good). Water clarity: 21 ft visibility. Phosphorus: 11.5 µg/L. Maximum depth: 82 ft. Surface area: 114 acres.
Wisconsin DNR rates Panfish as abundant on Sea Lion Lake. DNR survey details →
- Clarity
- 21 ft
- Typical in August
- 75°F
- Max depth
- 82 ft
- Area
- 114 acres
- Type
- Oligotrophic
- Trend
- ↓ Declining
- Public access
- Yes
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Sea Lion Lake is a 114-acre cold, clear oligotrophic lake in Florence County, Wisconsin with a maximum depth of 82 feet. Water quality is graded B based on 1 sampling years through 2026. Overall water quality is declining over recent sampling years. The lake supports 5 documented fish species including Panfish, Largemouth Bass, and Smallmouth Bass. Public access is available with 1 public boat landing. Compared to the 11 other monitored lakes in Florence County, Sea Lion Lake ranks #6 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-07-03. Grade methodology: LakeQuality 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.
Good for swimming, clear water with low algae levels
Water Quality Grade: B (Good)
Crystal clear, you can see 21 ft down. Phosphorus level: 11.5 µg/L. Trophic State Index: 36.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 21 ft | Not graded |
| Phosphorus | 11.5 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 36 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Sea Lion Lake
Compare lakeside cabins, hotels, and vacation rentals near Sea Lion 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 Sea Lion Lake
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Water Temperature
Sea Lion Lake typically sits around 75°F at the surface in August. Summer average is about 74°F. Usually warmest in Jul (about 75°F) and coldest in May (about 59°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 17 field readings (2024–2026) via the EPA Water Quality Portal. See the full Sea Lion Lake water temperature breakdown →
Wisconsin DNR rates Panfish as abundant on Sea Lion Lake.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Sea Lion Lake B from EPA Water Quality Portal chemistry, and the water-quality trend over 7 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 2020. 1 station on file (most recent sample 2025).
Fish Species (DNR-rated)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 82 ft |
| Surface Area | 114 acres |
| Public Access | Yes |
Recreation & Access
- Sea Lion LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Sea Lion 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.
Water Quality Trend: ↓ Declining
Based on 7 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.661 m/yr | 7 |
| Phosphorus | ↓ Declining | +3 µg/L/yr | 3 |
County Ranking
Ranked #6 of 12 lakes in Florence County
Nearby Lakes in Florence County
Frequently asked questions about Sea Lion Lake
Where is Sea Lion Lake?
- Sea Lion Lake is a lake in Florence County, Wisconsin. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Sea Lion Lake?
- Sea Lion Lake in Florence County, Wisconsin has a water quality grade of B (Good). Water clarity: 21 ft visibility. Phosphorus: 11.5 µg/L. Maximum depth: 82 ft. Surface area: 114 acres.
Is Sea Lion Lake safe to swim in?
- Good for swimming, clear water with low algae levels. Sea Lion Lake has a water quality grade of B (Good). Always check local health department advisories before swimming.
What is the water temperature of Sea Lion Lake?
- Sea Lion Lake typically sits around 75°F at the surface in August, from 17 EPA Water Quality Portal field readings (2024–2026). That is a typical value for the month, not a live reading.
How deep is Sea Lion Lake?
- Sea Lion Lake has a maximum depth of 82 feet. The lake covers 114 acres.
What fish are in Sea Lion Lake?
- Fish species found in Sea Lion Lake include Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye. Sea Lion Lake is located in Florence County, Wisconsin.
What did the DNR fisheries survey find at Sea Lion Lake?
- Wisconsin DNR rates Panfish as abundant on Sea Lion Lake. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Sea Lion Lake B from EPA Water Quality Portal chemistry, and the water-quality trend over 7 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
Are there boat ramps on Sea Lion Lake?
- Sea Lion Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Sea Lion Lake. Public access is listed as yes.
Explore Sea Lion Lake across LakeQuality
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Species activity outlook by water temperature and season
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Where this data comes from
44 measurements from 1 monitoring station, 2020–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX44 samples · 2020–2026
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