Oconomowoc Lake
Oconomowoc Lake in Waukesha County, Wisconsin has a water quality grade of B (Good). Water clarity: 12.5 ft visibility. Phosphorus: 11.9 µg/L. Maximum depth: 60 ft. Surface area: 818 acres.
Wisconsin DNR lists Largemouth Bass as common on Oconomowoc Lake. DNR survey details →
- Clarity
- 12.5 ft
- Max depth
- 60 ft
- Area
- 818 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
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Oconomowoc Lake is a 818-acre mesotrophic lake in Waukesha County, Wisconsin with a maximum depth of 60 feet. Water quality is graded B based on 1 sampling years through 2026. Overall water quality is improving over recent sampling years. The lake supports 5 documented fish species including Panfish, Largemouth Bass, and Smallmouth Bass. Compared to the 34 other monitored lakes in Waukesha County, Oconomowoc Lake ranks #19 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-23. 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 12.5 ft. Phosphorus level: 11.9 µg/L. Trophic State Index: 40.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 12.5 ft | Not graded |
| Phosphorus | 11.9 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 40 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Oconomowoc Lake
Compare lakeside cabins, hotels, and vacation rentals near Oconomowoc Lake in Waukesha 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.
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Oconomowoc Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was moderate (28,840 cells/mL) on April 5, 2026.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Wisconsin DNR lists Largemouth Bass as common on Oconomowoc Lake.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Oconomowoc Lake B from EPA Water Quality Portal chemistry, and the water-quality trend over 7 years of monitoring is improving. 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 1986. 26 stations on file (most recent sample 2025).
Fish Species (DNR-rated)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 60 ft |
| Surface Area | 818 acres |
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Oconomowoc 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.
Source: USGS Nonindigenous Aquatic Species (NAS) Database. Hover a chip to see scientific name, ecological context, status, and first-observed year.
Water Quality Trend: ↑ Improving
Based on 7 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.384 m/yr | 7 |
| Phosphorus | ↑ Improving | -0.46 µg/L/yr | 7 |
| Chlorophyll-a | ↑ Improving | -0.11 µg/L/yr | 4 |
Reservoir Info (USACE NID)
Oconomowoc Lake is a man-made reservoir impounded by the Oconomowoc Lake (completed 1899), built primarily for recreation on the OUTLET OCONOMOWOC LAKE; gravity-type dam, 7 ft tall and 60 ft long.
- Surface area
- 721 ac
- Normal storage
- 5,000 ac-ft
- Max storage
- 1,810 ac-ft
- Drainage area
- 87 sq mi
- Hazard class
- Low
- Owner
- VILLAGE OF OCONOMOWOC LAKE
Source: USACE National Inventory of Dams, NID ID WI01144 · Operator website
County Ranking
Ranked #19 of 35 lakes in Waukesha County
Nearby Lakes With Higher Grades
Oconomowoc Lake holds Grade B. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Waukesha County
Frequently asked questions about Oconomowoc Lake
Where is Oconomowoc Lake?
- Oconomowoc Lake is a lake in Waukesha County, Wisconsin. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Oconomowoc Lake?
- Oconomowoc Lake in Waukesha County, Wisconsin has a water quality grade of B (Good). Water clarity: 12.5 ft visibility. Phosphorus: 11.9 µg/L. Maximum depth: 60 ft. Surface area: 818 acres.
Is Oconomowoc Lake safe to swim in?
- Good for swimming, clear water with low algae levels. Oconomowoc Lake has a water quality grade of B (Good). Always check local health department advisories before swimming.
How deep is Oconomowoc Lake?
- Oconomowoc Lake has a maximum depth of 60 feet. The lake covers 818 acres.
What fish are in Oconomowoc Lake?
- Fish species found in Oconomowoc Lake include Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye. Oconomowoc Lake is located in Waukesha County, Wisconsin.
What did the DNR fisheries survey find at Oconomowoc Lake?
- Wisconsin DNR lists Largemouth Bass as common on Oconomowoc Lake. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Oconomowoc Lake B from EPA Water Quality Portal chemistry, and the water-quality trend over 7 years of monitoring is improving. Catch rate is not a swim clearance and is not a weekly bite report.
Does Oconomowoc Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Oconomowoc Lake (clouds, ice, or an off-season gap). The most recent reading was moderate (28,840 cells/mL). Blue-green algae can appear and clear within days, so check Wisconsin's current advisory before swimming.
Explore Oconomowoc Lake across LakeQuality
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Moderate nutrients, good water quality
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Where this data comes from
87 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_WQX87 samples · 2020–2026
Analytical methods
- Phosphorus by Colorimetry
- Total Phosphorus After Block Digestion
- 2130 B ~ Nephelometric Method
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