Roberts Lake
Forest County, WisconsinMesotrophic
Roberts Lake sits at the top of the Wisconsin DNR grading rubric with an A, a mark reached by the cleanest lakes in Wisconsin. clarity and phosphorus rate similarly, so there is no obvious single lever to pull on watershed management.
A TSI near 40 places Roberts Lake in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. A maximum depth of 31 ft puts Roberts Lake in the middle of Wisconsin's depth distribution. At 435 acres, Roberts Lake fits the Wisconsin median for monitored lakes, with partial shoreline records. Among the 34 graded lakes in Forest County, Roberts Lake sits at rank 10, above the county median.
Zebra mussel presence at Roberts Lake means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. Walleye are documented at Roberts Lake, one of 6 fish species on record for the lake. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-09-01. Grade methodology: LakeGrade methodology.
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Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Good clarity, visible to about 11.7 ft. Phosphorus level: 10.8 µg/L. Trophic State Index: 40.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 11.7 ft | B |
| Phosphorus | 10.8 µg/L | A |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 40 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 31 ft |
| Surface Area | 435 acres |
Fish Species
Click a species to see all Wisconsin and Minnesota lakes where it is found.
→ Best fishing times for Roberts Lake (14-day solunar calendar)
→ Is it safe to eat fish from Roberts Lake? (mercury & PFAS guide)
→ Roberts Lake fishing regulations (limits, seasons, special rules)
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 5 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.578 m/yr | 5 |
| Phosphorus | ↑ Improving | -3.5 µg/L/yr | 2 |
Location
County Ranking
Ranked #10 of 34 lakes in Forest County
Nearby Lakes in Forest County
More Wisconsin Lake Rankings
Other Grade A Lakes in Wisconsin
Washington County · Clarity: 11.8 ft
Washington County · Clarity: 12.6 ft
Walworth County · Clarity: 11 ft
Waukesha County · Clarity: 11.3 ft
Walworth County · Clarity: 20.2 ft
Kenosha County · Clarity: 10 ft
Mesotrophic Lakes in Wisconsin
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 1995. 1 station on file (most recent sample 2025).
Fish Species (DNR-rated)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Roberts Lake covering fish populations, stocking, water quality, and management. 1 report on file.
- 2022Roberts Lake fisheries summary, 2022Fisheries Survey · WI DNR · 2022 (PDF)
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Most recent sample: 2025-09-01
Monitoring stations: 1