Diamond Lake
Bayfield County, Wisconsin322 acresView mapDirections
Wisconsin DNR publishes the water-quality measurements for Diamond Lake. Here is what has been measured.
- Oligotrophic
- Impaired · Mercury
- 83 ft max depth
- Public access
Diamond Lake in Bayfield County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. 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 →
Diamond Lake is a 322-acre cold, clear oligotrophic lake in Bayfield County, Wisconsin with a maximum depth of 83 feet. 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 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. Methodology: how these readings are compared.
What Diamond Lake is good for
From access and monitoring records, not editorial picks.
- Clear water13 ft of visibility
- Boat launch1 documented ramp
- Fishing5 species recorded
- Deep water83 ft surveyed max depth
Swimming conditions
Readings onlyLow algae
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Diamond Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
Whether Diamond Lake is safe to swim in today is a call for the Wisconsin Department of Natural Resources and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Diamond Lake
These are the measurements Wisconsin DNR publishes for Diamond Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Good clarity, visible to about 13 ft. Phosphorus 11.8 µg/L. TSI 40.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 13ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 11.8µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 40 | Oligotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Low nutrients, clear water. No reading is a swimming clearance.
Ask about Diamond Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Diamond Lake typically sits around 66°F at the surface in September. 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.
Column height runs from this lake’s coldest month (66°F) to its warmest (76°F).
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 water quality. LakeQuality shows Diamond Lake’s water-quality measurements separately, 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
Max depth
83 ft
Surface area
322 acres
Public access
Yes
Listed by Wisconsin DNR
Lake Size & Watershed
Watershed (drainage) area
7 sq mi
HydroLAKES / HydroSHEDS
Shoreline
4.2 mi
HydroLAKES / HydroSHEDS
Elevation
1,388 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Diamond LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays 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
Prices for Oct 9–11, 4 adults. Change dates on the map below.
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 Wisconsin’s top lakes →
Follow Diamond Lake’s readings
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Fish Species
Click a species to see every 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: Worsening
Based on 6 years of monitoring (2020–2025).
Water clarity
Stable6 years
Phosphorus
Worsening+2.54 µg/L/yr6 years
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
Designated uses not supporting: Fish consumption.
Source: EPA ATTAINS assessment unit WI10026588 · Official waterbody report
Nearby Lakes in Bayfield County
Frequently asked questions about Diamond Lake
Where is Diamond Lake?
- Diamond Lake is a lake in Bayfield County, Wisconsin. Its water-quality measurements are published by Wisconsin DNR and shown on this page as reported.
What is the water quality of Diamond Lake?
- Diamond Lake in Bayfield County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. 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?
- Nutrient and algae readings are not a swimming clearance. Diamond Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
What is the water temperature of Diamond Lake?
- Diamond Lake typically sits around 66°F at the surface in September, 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 water quality. LakeQuality shows Diamond Lake’s water-quality measurements separately, 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.
Are there boat ramps on Diamond Lake?
- Diamond Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Diamond Lake. Public access is listed as yes.
Can I fish at Diamond Lake?
- Diamond Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Wisconsin's fish and wildlife agency, so check its current regulations before you go.
Explore Diamond Lake across LakeQuality
Depth, room, public access, and the state wake-sport rules
Fish species and the cleanest lakes across Wisconsin
Fish species and best lakes in Bayfield County
Species activity outlook by water temperature and season
Top lakes and where to stay in the Hayward Lakes area
Where to stay at Wisconsin's top lakes, each with its readings
Lakes in the Lake Superior Basin (MN+WI), ranked by water quality
Wisconsin's cleanest lakes, ranked on agency measurements
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Other Lakes in Wisconsin
Oligotrophic Lakes in Wisconsin
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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from 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
Named boat-access points from the USGS National Boat Ramps inventory