Diamond Lake
Diamond Lake in Bayfield County, Wisconsin has a water quality grade of B (Good). Water clarity: 13 ft visibility. Phosphorus: 11.8 µg/L. Maximum depth: 83 ft. Surface area: 322 acres.
Wisconsin DNR lists Panfish as common on Diamond Lake. DNR survey details →
- Clarity
- 13 ft
- Typical in August
- 71°F
- Max depth
- 83 ft
- Area
- 322 acres
- Type
- Oligotrophic
- Trend
- ↓ Declining
- Public access
- Yes
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Diamond Lake is a 322-acre cold, clear oligotrophic lake in Bayfield County, Wisconsin with a maximum depth of 83 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. Compared to the 23 other monitored lakes in Bayfield County, Diamond Lake ranks #6 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-04-22. 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)
Good clarity, visible to about 13 ft. Phosphorus level: 11.8 µg/L. Trophic State Index: 40.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 13 ft | Not graded |
| Phosphorus | 11.8 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 40 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Diamond Lake
Compare lakeside cabins, hotels, and vacation rentals near Diamond Lake in Bayfield 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 Diamond Lake
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Water Temperature
Diamond Lake typically sits around 71°F at the surface in August. Summer average is about 74°F. Usually warmest in Jul (about 76°F) and coldest in Sep (about 66°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 12 field readings (2024–2025) via the EPA Water Quality Portal. See the full Diamond Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Diamond Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was high (147,231 cells/mL) on October 11, 2025.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Wisconsin DNR lists Panfish as common on Diamond Lake.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Diamond Lake B from EPA Water Quality Portal chemistry, and the water-quality trend over 6 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 1992. 2 stations on file (most recent sample 2025).
Fish Species (DNR-rated)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Diamond Lake covering fish populations, stocking, water quality, and management. 2 reports on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- 2024Diamond Lake comprehensive survey, 2024Comprehensive Survey · WI DNR · 2024 (PDF)
- 2018Diamond Lake comprehensive fisheries survey, 2018Comprehensive Survey · WI DNR · 2018 (PDF)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 83 ft |
| Surface Area | 322 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Diamond 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 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | -0.129 m/yr | 6 |
| Phosphorus | ↓ Declining | +2.54 µg/L/yr | 6 |
EPA Impairment Status
Diamond 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 WI10026588 · Official waterbody report
County Ranking
Ranked #6 of 24 lakes in Bayfield County
Nearby Lakes in Bayfield County
Frequently asked questions about Diamond Lake
Where is Diamond Lake?
- Diamond Lake is a lake in Bayfield County, Wisconsin. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Diamond Lake?
- Diamond Lake in Bayfield County, Wisconsin has a water quality grade of B (Good). Water clarity: 13 ft visibility. Phosphorus: 11.8 µg/L. Maximum depth: 83 ft. Surface area: 322 acres.
Is Diamond Lake safe to swim in?
- Good for swimming, clear water with low algae levels. Diamond Lake has a water quality grade of B (Good). Always check local health department advisories before swimming.
What is the water temperature of Diamond Lake?
- Diamond Lake typically sits around 71°F at the surface in August, from 12 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Diamond Lake?
- Diamond Lake has a maximum depth of 83 feet. The lake covers 322 acres.
What fish are in Diamond Lake?
- Fish species found in Diamond Lake include Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye. Diamond Lake is located in Bayfield County, Wisconsin.
What did the DNR fisheries survey find at Diamond Lake?
- Wisconsin DNR lists Panfish as common on Diamond Lake. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Diamond Lake B from EPA Water Quality Portal chemistry, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
Does Diamond Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Diamond Lake (clouds, ice, or an off-season gap). The most recent reading was high (147,231 cells/mL). Blue-green algae can appear and clear within days, so check Wisconsin's current advisory before swimming.
Explore Diamond Lake across LakeQuality
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Where this data comes from
66 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_WQX66 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
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Fish and recreation data from Wisconsin DNR Lakes