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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.

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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.

MetricValueGrade
Water Clarity (Secchi Depth)10.5 ftB
Phosphorus11.1 µg/LA
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)41Mesotrophic

Moderate nutrients, good water quality

Lake Details

CharacteristicValue
Maximum Depth28 ft
Surface Area48 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.

Banded Mystery SnailChinese Mystery Snail

Water Quality Trend: Stable

Based on 6 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Water Clarity Declining-0.873 m/yr6
Phosphorus Improving-0.93 µg/L/yr6
See year-by-year chart →

Location

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County Ranking

Ranked #10 of 28 lakes in Portage County

Nearby Lakes in Portage County

WI DNR Lake Profile

Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 2013. 1 station on file (most recent sample 2025).

DNR Assessment
Excellent · Deep Seepage lake
Trophic State Index 39 (oligotrophic) · 5-year average

Fish Species (DNR-rated)

Panfish(Common)Largemouth Bass(Common)Northern Pike(Present)

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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