Oconomowoc Lake
Waukesha County, Wisconsin818 acresView mapDirections
Wisconsin DNR publishes the water-quality measurements for Oconomowoc Lake. Here is what has been measured.
- Mesotrophic
- Zebra Mussel
- 60 ft max depth
Oconomowoc Lake in Waukesha County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. 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 →
Oconomowoc Lake is a 818-acre mesotrophic lake in Waukesha County, Wisconsin with a maximum depth of 60 feet. 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. Methodology: how these readings are compared.
Oconomowoc Lake covers about 820 acres in Waukesha County. For a place on the water, look through cabin and lake-house rentals near Oconomowoc Lake on Vrbo. For a hotel or motel room, Booking.com and Expedia both search around the lake.
What Oconomowoc Lake is good for
From access and monitoring records, not editorial picks.
- Clear water12.5 ft of visibility
- Fishing5 species recorded
- Deep water60 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. Check local advisories before you swim.
Whether Oconomowoc 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 Oconomowoc Lake
These are the measurements Wisconsin DNR publishes for Oconomowoc 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 12.5 ft. Phosphorus 11.9 µg/L. TSI 40.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 12.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 11.9µg/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 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Oconomowoc Lake
Answers come straight from the public measurements and survey records on this page.
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 water quality. LakeQuality shows Oconomowoc Lake’s water-quality measurements separately, 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
Max depth
60 ft
Surface area
818 acres
Stays via Stay22
Stays near Oconomowoc Lake
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Fish Species
Click a species to see every 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.
Water Quality Trend: Improving
Based on 7 years of monitoring (2020–2026).
Water clarity
Improving7 years
Phosphorus
Improving-0.46 µg/L/yr7 years
Chlorophyll-a
Improving-0.11 µg/L/yr4 years
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
Nearby Lakes in Waukesha County
Frequently asked questions about Oconomowoc Lake
Where is Oconomowoc Lake?
- Oconomowoc Lake is a lake in Waukesha County, Wisconsin. Its water-quality measurements are published by Wisconsin DNR and shown on this page as reported.
What is the water quality of Oconomowoc Lake?
- Oconomowoc Lake in Waukesha County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. 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?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
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 water quality. LakeQuality shows Oconomowoc Lake’s water-quality measurements separately, 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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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)
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
Fish and recreation data from Wisconsin DNR Lakes