Onland Lake
Portage County, WisconsinMesotrophic
Onland Lake sits at the top of the Wisconsin DNR grading rubric with an A, a mark reached by the cleanest lakes in Wisconsin. Sub-grades cluster within a single letter of each other, which usually means the lake is in stable trophic balance rather than fighting one specific stressor.
The lake sits in the mesotrophic zone — the band where most well-managed Wisconsin lakes fall. A maximum depth of 28 ft puts Onland Lake in the middle of Wisconsin's depth distribution. Onland Lake is small — 48 acres alongside partial shoreline records — which makes it sensitive to even modest changes in watershed runoff or recreational pressure. Onland Lake ranks 10 of 28 in Portage County — solidly in the upper half of the local distribution.
Onland Lake has at least one documented invasive species (Banded Mystery Snail), so boaters and anglers should observe clean-drain-dry steps when leaving the lake. The fishery is bass-led, with 3 documented species across the lake's records. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-10-07. Grade methodology: LakeGrade methodology.
Watch Onland Lake water quality
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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 10.5 ft. Phosphorus level: 11.1 µg/L. Trophic State Index: 41.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 10.5 ft | B |
| Phosphorus | 11.1 µg/L | A |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 41 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 28 ft |
| Surface Area | 48 acres |
Fish Species
Click a species to see every graded lake where it is documented.
→ Best fishing times for Onland Lake (14-day solunar calendar)
→ Is it safe to eat fish from Onland Lake? (mercury & PFAS guide)
→ Onland 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: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.873 m/yr | 6 |
| Phosphorus | ↑ Improving | -0.93 µg/L/yr | 6 |
Location
County Ranking
Ranked #10 of 28 lakes in Portage County
Nearby Lakes in Portage County
More Wisconsin Lake Rankings
State Parks Near Onland Lake
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 2013. 1 station on file (most recent sample 2025).
Fish Species (DNR-rated)
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Fish and recreation data from Wisconsin DNR Lakes
Most recent sample: 2025-10-07
Monitoring stations: 1
Where to stay near Onland Lake
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