Big Round Lake
Big Round Lake in Polk County, Wisconsin has a water quality grade of C (Fair). Water clarity: 5 ft visibility. Phosphorus: 27 µg/L. Chlorophyll-a (algae): 6.9 µg/L. Maximum depth: 17 ft. Surface area: 1014 acres.
Wisconsin DNR rates Panfish as abundant on Big Round Lake. DNR survey details →
- Clarity
- 5 ft
- Typical in August
- 72°F
- Max depth
- 17 ft
- Area
- 1,014 acres
- Type
- Eutrophic
- Trend
- ↑ Improving
- Public access
- Yes
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Big Round Lake is a 1,014-acre productive, nutrient-rich eutrophic lake in Polk County, Wisconsin with a maximum depth of 17 feet. Water quality is graded C based on 3 sampling years through 2026. Overall water quality is improving over recent sampling years. The lake supports 5 documented fish species including Musky, Panfish, and Largemouth Bass. Public access is available with 1 public boat landing. Compared to the 54 other monitored lakes in Polk County, Big Round Lake ranks #28 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-21. Grade methodology: LakeGrade methodology.
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Swimming Safety
Grade onlyModerate
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.
Generally safe for swimming, moderate water quality
Water Quality Grade: C (Fair)
Murky, only visible to about 5 ft. Phosphorus level: 27 µg/L. Chlorophyll-a: 6.9 µg/L. Trophic State Index: 52.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5 ft | Not graded |
| Phosphorus | 27 µg/L | Fair |
| Chlorophyll-a (Algae) | 6.9 µg/L | Good |
| Trophic State Index (TSI) | 52 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Big Round Lake
Compare lakeside cabins, hotels, and vacation rentals near Big Round 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 Big Round Lake
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Planning a whole trip? See where to stay at Wisconsin’s top lakes →
Water Temperature
Big Round Lake typically sits around 72°F at the surface in August. Summer average is about 74°F. Usually warmest in Jul (about 78°F) and coldest in Apr (about 50°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 140 field readings (2024–2025) via the EPA Water Quality Portal. See the full Big Round Lake water temperature breakdown →
Blue-Green Algae (Cyanobacteria)
There’s no recent EPA CyAN cyanobacteria estimate for Big Round Lake — clouds, ice, or an off-season gap in coverage. The most recent reading was moderate (26,546 cells/mL) on October 25, 2025.
Blue-green algae can appear and clear within days, so check your state’s current advisory before swimming. EPA CyAN ↗
Wisconsin DNR rates Panfish as abundant on Big Round Lake.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Big Round Lake C 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 1992. 2 stations on file (most recent sample 2025).
Fish Species (DNR-rated)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 17 ft |
| Surface Area | 1,014 acres |
| Public Access | Yes |
Recreation & Access
- Big Round LakePublic
Named access points from the USGS National Boat Ramps inventory, snapped within 5 km. More lakes with boat ramps
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Big Round 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 | +0.484 m/yr | 6 |
| Phosphorus | ↑ Improving | -8.95 µg/L/yr | 7 |
| Chlorophyll-a | ↑ Improving | -12.08 µg/L/yr | 6 |
EPA Impairment Status
Big Round Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5R).
Causes of impairment
Source: EPA ATTAINS assessment unit WI10005037 · Official waterbody report
County Ranking
Ranked #28 of 55 lakes in Polk County
Nearby Lakes With Higher Grades
Big Round Lake holds Grade C. 2 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Polk County
Frequently asked questions about Big Round Lake
Where is Big Round Lake?
- Big Round Lake is a lake in Polk County, Wisconsin. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Big Round Lake?
- Big Round Lake in Polk County, Wisconsin has a water quality grade of C (Fair). Water clarity: 5 ft visibility. Phosphorus: 27 µg/L. Chlorophyll-a (algae): 6.9 µg/L. Maximum depth: 17 ft. Surface area: 1014 acres.
Is Big Round Lake safe to swim in?
- Generally safe for swimming, moderate water quality. Big Round Lake has a water quality grade of C (Fair). Algae concentration (chlorophyll-a) is 6.9 µg/L. Always check local health department advisories before swimming.
What is the water temperature of Big Round Lake?
- Big Round Lake typically sits around 72°F at the surface in August, from 140 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading.
How deep is Big Round Lake?
- Big Round Lake has a maximum depth of 17 feet. The lake covers 1014 acres.
What fish are in Big Round Lake?
- Fish species found in Big Round Lake include Musky, Panfish, Largemouth Bass, Northern Pike, Walleye. Big Round Lake is located in Polk County, Wisconsin.
What did the DNR fisheries survey find at Big Round Lake?
- Wisconsin DNR rates Panfish as abundant on Big Round Lake. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Big Round Lake C 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.
Does Big Round Lake have blue-green algae?
- There is no recent EPA CyAN cyanobacteria estimate for Big Round Lake (clouds, ice, or an off-season gap). The most recent reading was moderate (26,546 cells/mL). Blue-green algae can appear and clear within days, so check Wisconsin's current advisory before swimming.
Are there boat ramps on Big Round Lake?
- Big Round Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Big Round Lake. Public access is listed as yes.
Explore Big Round Lake across LakeGrade
Depth, room, public access, and the state wake-sport rules
Fish species and top-graded lakes across Wisconsin
Fish species and best lakes in Polk County
Species activity outlook by water temperature and season
Where to stay at Wisconsin's top lakes, each with its grade
Lakes in the St. Croix Watershed, ranked by water quality
High nutrients, frequent algae, reduced clarity
Wisconsin's cleanest and most-polluted lakes, ranked
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Eutrophic Lakes in Wisconsin
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Where this data comes from
606 measurements from 3 monitoring stations, 2020–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- St. Croix Chippewa Indians of Wisconsin
STCROIX_WQX342 samples · 2020–2025 - Wisconsin Department of Natural Resources
WIDNR_WQX264 samples · 2020–2026
Analytical methods
- Phosphorus by Colorimetry
- 4500 P E ~ Phosphorus in Water by Colorimetry- Ascorbic Acid Method
- 4500 P F ~ Phosphorus in Water by Colorimetry Automated Ascorbic Acid Method
- 10200 H ~ Chlorophyll a-b-c Determination
- Calculation
Monitoring station identifiers (3)
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
Impairment status from EPA ATTAINS 303(d) database
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