Where is Ottawa Lake?

Ottawa Lake is a lake in Waukesha County, Wisconsin. Its water-quality measurements are published by Wisconsin DNR and shown on this page as reported.

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 is a historical summary of past bacteria testing, not a current reading and not a swimming clearance. Bacteria levels can spike quickly after heavy rain, so whether Ottawa Lake is safe to swim in today is a call for Wisconsin's water agency and the county health department; check their current beach advisories before you swim.

What is the water temperature of Ottawa Lake?

Ottawa Lake typically sits around 71°F at the surface in September, 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.

Are there boat ramps on Ottawa Lake?

Ottawa Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Ottawa Lake. Public access is listed as yes.

Can I fish at Ottawa Lake?

Ottawa 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.

Ottawa Lake

Waukesha County, Wisconsin17 acresView map Directions

Wisconsin DNR publishes the water-quality measurements for Ottawa Lake. Here is what has been measured.

Clarity

13 ft

Clearer than most

Secchi · sampled 2026

Phosphorus

14.6 µg/L

Typical for Wisconsin

Measured by Wisconsin DNR

Water temp

~71°F

Typical for Sep · EPA WQP

Max depth

16 ft

Bathymetric survey

Area

17 acres

Surface area

Type

Mesotrophic

Trophic class

Mesotrophic
2 aquatic invasives
16 ft max depth
Public access

See the measurements Directions Where to stay

Ottawa Lake in Waukesha County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. 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 →

Loading map…

Ottawa Lake is a 17-acre mesotrophic lake in Waukesha County, Wisconsin with a maximum depth of 16 feet. 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 1 public boat landing. 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. Methodology: how these readings are compared.

Ottawa Lake covers about 17 acres in Waukesha County. It has one public boat landing. For a place on the water, look through cabin and lake-house rentals near Ottawa Lake on Vrbo. For a hotel or motel room, Booking.com and Expedia both search around the lake.

What Ottawa Lake is good for

From access and monitoring records, not editorial picks.

Clear water13 ft of visibility
Boat launch1 documented ramp
Fishing4 species recorded

Swimming conditions

Readings only

Bacteria tested: exceedances

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.

Bacteria testing record

from E. coli testing · 440 samples, 9 seasons

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.

Whether Ottawa 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.

Compare swimming lakes near Milwaukee →

Get alerts for Ottawa Lake →

Water quality measurements for Ottawa Lake

These are the measurements Wisconsin DNR publishes for Ottawa 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 14.6 µg/L. TSI 41.

Water quality readings
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	14.6µg/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.	41	Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic

Moderate nutrients, good water quality

Ask about Ottawa Lake

Answers come straight from the public measurements and survey records on this page.

Water Temperature

Ottawa Lake typically sits around 71°F at the surface in September. 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.

Jan

Feb

Mar

Apr

65°

May

79°

Jun

79°

Jul

77°

Aug

71°

Sep

Oct

Nov

Dec

Column height runs from this lake’s coldest month (65°F) to its warmest (79°F).

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 →

DNR fisheries survey

Wisconsin DNR lists Panfish as common on Ottawa Lake.

A DNR fisheries survey reports fish abundance and catch rates, not water quality. LakeQuality shows Ottawa 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 2002. 2 stations on file (most recent sample 2025).

DNR Assessment

Excellent · Deep Headwater lake

Trophic State Index 40 (oligotrophic) · 5-year average

Fish Species (DNR-rated)

Panfish(Common)Largemouth Bass(Present)Northern Pike(Present)Walleye(Present)

Contour map (PDF) →Full WI DNR LakePage →Water quality stations →

Lake Details

Max depth

16 ft

Surface area

17 acres

Public access

Yes

Listed by Wisconsin DNR

Lake Size & Watershed

Watershed (drainage) area

3 sq mi

HydroLAKES / HydroSHEDS

Shoreline

1.1 mi

HydroLAKES / HydroSHEDS

Elevation

860 ft

Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).

Recreation & Access

Boat Landings

Yes

Public Access

Ottawa 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 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

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 Ottawa Lake’s readings

Email me when new measurements post for this lake. Updates stay free.

Or email

Fish Species

Panfish Largemouth Bass Northern Pike Walleye

Click a species to see every 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.

Curly-Leaf PondweedPurple Loosestrife

Water Quality Trend: Improving

Based on 7 years of monitoring (2020–2026).

Water clarity
Stable
6 years
Phosphorus
Improving
-0.61 µg/L/yr7 years

See year-by-year chart →

Nearby Lakes in Waukesha County

Pretty Lake12.2 ft clear · Mesotrophic—View →Larkin Lake—View →School Section Lake6.2 ft clear · Eutrophic—View →Hunters Lake9.5 ft clear · Mesotrophic—View →Dutchman Lake—View →Henrietta Lake—View →

Frequently asked questions about Ottawa Lake

Where is Ottawa Lake?: Ottawa 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 Ottawa Lake?: Ottawa Lake in Waukesha County, Wisconsin has water-quality measurements published by Wisconsin DNR, shown here as reported. 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 is a historical summary of past bacteria testing, not a current reading and not a swimming clearance. Bacteria levels can spike quickly after heavy rain, so whether Ottawa Lake is safe to swim in today is a call for Wisconsin's water agency and the county health department; check their current beach advisories before you swim.
What is the water temperature of Ottawa Lake?: Ottawa Lake typically sits around 71°F at the surface in September, 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 water quality. LakeQuality shows Ottawa 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.
Are there boat ramps on Ottawa Lake?: Ottawa Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Ottawa Lake. Public access is listed as yes.
Can I fish at Ottawa Lake?: Ottawa 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 Ottawa Lake across LakeQuality

Wisconsin Fishing Guide

Fish species and the cleanest lakes across Wisconsin

Waukesha County Fishing

Fish species and best lakes in Waukesha County

Lake Fishing Forecast

Species activity outlook by water temperature and season

Wisconsin Lake Trips

Where to stay at Wisconsin's top lakes, each with its readings

The State of Wisconsin's Lakes

Wisconsin's cleanest lakes, ranked on agency measurements

More lakes in Wisconsin

Clearest lakes in Wisconsin

Ranked by Secchi water clarity

All Wisconsin lakes

Every Wisconsin lake with its Wisconsin DNR measurements

Lake water quality by country

Official ratings and named-lake measurements

State Parks Near Ottawa Lake

Aztalan State Park

State Park · 21.2 mi

Other Lakes in Wisconsin

Blue Spring Lake

Jefferson County · 6.2 ft

Booth Lake

Walworth County · 8 ft

Army Lake

Walworth County · 8.2 ft

Pleasant Lake

Walworth County · 12 ft

Potter Lake

Walworth County · 4.3 ft

Green Lake

Walworth County · 11 ft

Mesotrophic Lakes in Wisconsin

Peters Lake Pickerel Lake Swan Lake Booth Lake

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 ResourcesWIDNR_WQX80 samples · 2020–2026

Analytical methods

Phosphorus by Colorimetry

Monitoring station identifiers (1)

WIDNR_WQX-683202

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.