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LakeQuality
D

Long Lake

Manitowoc County, WisconsinEutrophic

On the scoring rubric Long Lake grades a D: clarity at 5.2 ft and 90 µg/L of phosphorus keep it in the lower bracket for Manitowoc County. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

At a TSI of 61, Long Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. A maximum depth of 38 ft puts Long Lake in the middle of Wisconsin's depth distribution. The lake's 119 acres and partial shoreline records put it in the mid-range bucket — large enough for varied use, small enough that watershed inputs reach the whole basin. Within the 18 graded lakes of Manitowoc County, Long Lake sits at rank 18, near the bottom of the county list.

Eurasian watermilfoil is established at Long Lake, which can dampen recreational access and pressure the native plant community. The fishery is bass-led, with 3 documented species across the lake's records. Public access is available — the lake is on the Wisconsin DNR public-access list. 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 2025-08-25. Grade methodology: LakeGrade methodology.

Swimming Safety

Swimming not recommended, poor water quality with high algae risk

Water Quality Grade: D, Poor

Murky, only visible to about 5.2 ft. Phosphorus level: 90.4 µg/L. Trophic State Index: 61.

MetricValueGrade
Water Clarity (Secchi Depth)5.2 ftD
Phosphorus90.4 µg/LF
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)61Eutrophic

High nutrients, frequent algae, reduced clarity

Lake Details

CharacteristicValue
Maximum Depth38 ft
Surface Area119 acres
Public AccessYes

Fish Species

Click a species to see all Wisconsin and Minnesota lakes where it is found.

→ Best fishing times for Long Lake (14-day solunar calendar)

→ Is it safe to eat fish from Long Lake? (mercury & PFAS guide)

Long Lake fishing regulations (limits, seasons, special rules)

Invasive Species

Curly-Leaf PondweedEurasian Water-MilfoilPurple Loosestrife

Water Quality Trend: Improving

Based on 7 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Water Clarity Improving+0.105 m/yr7
Phosphorus Improving-2.85 µg/L/yr6

Recreation & Access

1
Boat Landings
Yes
Public Access

Location

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County Ranking

Ranked #18 of 18 lakes in Manitowoc County

Nearby Lakes in Manitowoc County

Eutrophic Lakes in Wisconsin

WI DNR Lake Profile

Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 1992. 1 station on file (most recent sample 2025).

DNR Assessment
Poor · Deep Headwater lake
Trophic State Index 73 (hypereutrophic) · 5-year average

Fish Species (DNR-rated)

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

DNR Reports & Resources

Wisconsin DNR Fisheries scientists publish multi-year survey reports for Long Lake covering fish populations, stocking, water quality, and management. 1 report on file.

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: 2025-08-25

Monitoring stations: 1