Lower Nemahbin Lake
Lower Nemahbin Lake in Waukesha County, Wisconsin has a water quality grade of B (Good). Water clarity: 10.9 ft visibility. Phosphorus: 10.9 µg/L. Maximum depth: 36 ft. Surface area: 239 acres.
- Clarity
- 10.9 ft
- Typical in August
- 77°F
- Max depth
- 36 ft
- Area
- 239 acres
- Type
- Mesotrophic
- Trend
- ↑ Improving
- Public access
- Yes
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Lower Nemahbin Lake is a 239-acre mesotrophic lake in Waukesha County, Wisconsin with a maximum depth of 36 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. Public access is available. Compared to the 34 other monitored lakes in Waukesha County, Lower Nemahbin Lake ranks #24 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-07. 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 10.9 ft. Phosphorus level: 10.9 µg/L. Trophic State Index: 41.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 10.9 ft | Not graded |
| Phosphorus | 10.9 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 41 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Lower Nemahbin Lake
Compare lakeside cabins, hotels, and vacation rentals near Lower Nemahbin 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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Water Temperature
Lower Nemahbin Lake typically sits around 77°F at the surface in August. Summer average is about 78°F. Usually warmest in Jun (about 78°F) and coldest in Apr (about 54°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 9 field readings (2024–2025) via the EPA Water Quality Portal. See the full Lower Nemahbin Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 36 ft |
| Surface Area | 239 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Lower Nemahbin 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 | ↑ Improving | +0.38 m/yr | 7 |
| Phosphorus | ↑ Improving | -0.5 µg/L/yr | 7 |
Reservoir Info (USACE NID)
Lower Nemahbin Lake is a man-made reservoir impounded by the Lower Lake Nemahbin (completed 1934), built primarily for recreation on the BARK; gravity-type dam, 8 ft tall and 200 ft long.
- Surface area
- 268 ac
- Normal storage
- 270 ac-ft
- Max storage
- 1,880 ac-ft
- Drainage area
- 54 sq mi
- Hazard class
- Low
- Owner
- Village Of Summit
Source: USACE National Inventory of Dams, NID ID WI01120 · Operator website
County Ranking
Ranked #24 of 35 lakes in Waukesha County
Nearby Lakes in Waukesha County
Frequently asked questions about Lower Nemahbin Lake
Where is Lower Nemahbin Lake?
- Lower Nemahbin 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 Lower Nemahbin Lake?
- Lower Nemahbin Lake in Waukesha County, Wisconsin has a water quality grade of B (Good). Water clarity: 10.9 ft visibility. Phosphorus: 10.9 µg/L. Maximum depth: 36 ft. Surface area: 239 acres.
Is Lower Nemahbin Lake safe to swim in?
- Good for swimming, clear water with low algae levels. Lower Nemahbin Lake has a water quality grade of B (Good). Always check local health department advisories before swimming.
What is the water temperature of Lower Nemahbin Lake?
- Lower Nemahbin Lake typically sits around 77°F at the surface in August, from 9 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Lower Nemahbin Lake?
- Lower Nemahbin Lake has a maximum depth of 36 feet. The lake covers 239 acres.
What fish are in Lower Nemahbin Lake?
- Fish species found in Lower Nemahbin Lake include Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye. Lower Nemahbin Lake is located in Waukesha County, Wisconsin.
Explore Lower Nemahbin Lake across LakeQuality
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Moderate nutrients, good water quality
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Where this data comes from
125 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_WQX125 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