Ottawa Lake
Ottawa Lake in Waukesha County, Wisconsin has a water quality grade of B (Good). Water clarity: 13 ft visibility. Phosphorus: 14.6 µg/L. Maximum depth: 16 ft. Surface area: 17 acres.
Wisconsin DNR lists Panfish as common on Ottawa Lake. DNR survey details →
- Clarity
- 13 ft
- Typical in August
- 77°F
- Max depth
- 16 ft
- Area
- 17 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
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Ottawa Lake is a 17-acre mesotrophic lake in Waukesha County, Wisconsin with a maximum depth of 16 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 4 documented fish species including Panfish, Largemouth Bass, and Northern Pike. Public access is available with 2 public boat landings. Compared to the 34 other monitored lakes in Waukesha County, Ottawa Lake ranks #10 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 onlyBacteria C
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.
Based on E. coli testing, Ottawa Lake occasionally exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 7.5% of 440 samples across 9 seasons.
This is a historical summary of past testing, not a current condition — bacteria levels change quickly, especially after rain. Always check Wisconsin’s current beach and health-department advisories before swimming.
Water Quality Grade: B (Good)
Good clarity, visible to about 13 ft. Phosphorus level: 14.6 µg/L. Trophic State Index: 41.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 13 ft | Not graded |
| Phosphorus | 14.6 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 41 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Ottawa Lake
Compare lakeside cabins, hotels, and vacation rentals near Ottawa 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.
Top-rated places to stay near Ottawa Lake
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Water Temperature
Ottawa Lake typically sits around 77°F at the surface in August. Summer average is about 78°F. Usually warmest in Jun (about 79°F) and coldest in May (about 65°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 16 field readings (2024–2025) via the EPA Water Quality Portal. See the full Ottawa Lake water temperature breakdown →
Wisconsin DNR lists Panfish as common on Ottawa Lake.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Ottawa 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 2002. 2 stations on file (most recent sample 2025).
Fish Species (DNR-rated)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 16 ft |
| Surface Area | 17 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Ottawa LakePublic
- Beaver Dam 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 Ottawa 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 data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.007 m/yr | 6 |
| Phosphorus | ↑ Improving | -0.61 µg/L/yr | 7 |
County Ranking
Ranked #10 of 35 lakes in Waukesha County
Nearby Lakes in Waukesha County
Frequently asked questions about Ottawa Lake
Where is Ottawa Lake?
- Ottawa 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 Ottawa Lake?
- Ottawa Lake in Waukesha County, Wisconsin has a water quality grade of B (Good). Water clarity: 13 ft visibility. Phosphorus: 14.6 µg/L. Maximum depth: 16 ft. Surface area: 17 acres.
Is Ottawa Lake safe to swim in?
- Based on E. coli testing, Ottawa Lake occasionally exceeded the EPA safe-swimming threshold (235 MPN/100mL) — on 7.5% of 440 samples across 9 seasons. That works out to a bacteria swim-safety grade of C — a historical summary of past testing, not a current reading. Ottawa Lake has a water quality grade of B (Good). Bacteria levels can spike quickly after heavy rain, so always check Wisconsin's current beach and health-department advisories before you swim.
What is the water temperature of Ottawa Lake?
- Ottawa Lake typically sits around 77°F at the surface in August, from 16 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Ottawa Lake?
- Ottawa Lake has a maximum depth of 16 feet. The lake covers 17 acres.
What fish are in Ottawa Lake?
- Fish species found in Ottawa Lake include Panfish, Largemouth Bass, Northern Pike, Walleye. Ottawa Lake is located in Waukesha County, Wisconsin.
What did the DNR fisheries survey find at Ottawa Lake?
- Wisconsin DNR lists Panfish as common on Ottawa Lake. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Ottawa 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.
Are there boat ramps on Ottawa Lake?
- Ottawa Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Ottawa Lake, Beaver Dam Lake. Public access is listed as yes.
Explore Ottawa Lake across LakeQuality
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Moderate nutrients, good water quality
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Where this data comes from
80 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_WQX80 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