Half Moon Lake
Half Moon Lake in Polk County, Wisconsin has a water quality grade of B (Good). Water clarity: 15.3 ft visibility. Phosphorus: 13.9 µg/L. Maximum depth: 60 ft. Surface area: 550 acres.
Wisconsin DNR rates Largemouth Bass as abundant on Half Moon Lake. DNR survey details →
- Clarity
- 15.3 ft
- Typical in August
- 73°F
- Max depth
- 60 ft
- Area
- 550 acres
- Type
- Oligotrophic
- Trend
- ↓ Declining
- Public access
- Yes
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Half Moon Lake is a 550-acre cold, clear oligotrophic lake in Polk County, Wisconsin with a maximum depth of 60 feet. Water quality is graded B based on 1 sampling years through 2025. Overall water quality is declining 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 54 other monitored lakes in Polk County, Half Moon Lake ranks #14 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-08-31. Grade methodology: LakeQuality methodology.
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Swimming Safety
Grade onlyLimited data
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)
Crystal clear, you can see 15.3 ft down. Phosphorus level: 13.9 µg/L. Trophic State Index: 40.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 15.3 ft | Not graded |
| Phosphorus | 13.9 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 40 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Half Moon Lake
Compare lakeside cabins, hotels, and vacation rentals near Half Moon Lake in Polk 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 Half Moon Lake
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Water Temperature
Half Moon Lake typically sits around 73°F at the surface in August. Summer average is about 72°F. Usually warmest in Jul (about 77°F) and coldest in Jun (about 67°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 Half Moon Lake water temperature breakdown →
Wisconsin DNR rates Largemouth Bass as abundant on Half Moon Lake.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Half Moon Lake B from EPA Water Quality Portal chemistry, and the water-quality trend over 6 years of monitoring is declining. 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 1993. 13 stations on file (most recent sample 2025).
Fish Species (DNR-rated)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 60 ft |
| Surface Area | 550 acres |
| Public Access | Yes |
Recreation & Access
- Bone 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 Half Moon 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: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | → Stable | +0.093 m/yr | 6 |
| Phosphorus | ↓ Declining | +5.8 µg/L/yr | 3 |
County Ranking
Ranked #14 of 55 lakes in Polk County
Nearby Lakes in Polk County
Frequently asked questions about Half Moon Lake
Where is Half Moon Lake?
- Half Moon Lake is a lake in Polk County, Wisconsin. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Half Moon Lake?
- Half Moon Lake in Polk County, Wisconsin has a water quality grade of B (Good). Water clarity: 15.3 ft visibility. Phosphorus: 13.9 µg/L. Maximum depth: 60 ft. Surface area: 550 acres.
Is Half Moon Lake safe to swim in?
- Good for swimming, clear water with low algae levels. Half Moon Lake has a water quality grade of B (Good). Always check local health department advisories before swimming.
What is the water temperature of Half Moon Lake?
- Half Moon Lake typically sits around 73°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 Half Moon Lake?
- Half Moon Lake has a maximum depth of 60 feet. The lake covers 550 acres.
What fish are in Half Moon Lake?
- Fish species found in Half Moon Lake include Panfish, Largemouth Bass, Northern Pike, Walleye. Half Moon Lake is located in Polk County, Wisconsin.
What did the DNR fisheries survey find at Half Moon Lake?
- Wisconsin DNR rates Largemouth Bass as abundant on Half Moon Lake. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Half Moon Lake B from EPA Water Quality Portal chemistry, and the water-quality trend over 6 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
Are there boat ramps on Half Moon Lake?
- Half Moon Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Bone Lake. Public access is listed as yes.
Explore Half Moon Lake across LakeQuality
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Fish species and best lakes in Polk County
Species activity outlook by water temperature and season
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Lakes in the St. Croix Watershed, ranked by water quality
Low nutrients, clear water, excellent for swimming
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Where this data comes from
33 measurements from 2 monitoring stations, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX33 samples · 2020–2025
Analytical methods
- Phosphorus by Colorimetry
Monitoring station identifiers (2)
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