What is the water quality grade for Fon-du-Lac Reservoir?

Fon-du-Lac Reservoir in Jefferson County, Wisconsin received a water quality grade of F (Very Poor). Water clarity: 1.3 ft visibility. Phosphorus: 81 µg/L. Chlorophyll-a (algae): 40.7 µg/L. Surface area: 26 acres.

Is Fon-du-Lac Reservoir safe to swim in?

Avoid swimming, very poor water quality, potential algae toxins. Fon-du-Lac Reservoir has an overall water quality grade of F. Algae concentration (chlorophyll-a) is 40.7 µg/L. Always check local health department advisories before swimming.

Fon-du-Lac Reservoir

Jefferson County, WisconsinEutrophic

Fon-du-Lac Reservoir is a 26-acre productive, nutrient-rich eutrophic lake in Jefferson County, MO. Water quality is graded F based on 3 sampling years through 2024. Compared to the 6 other monitored lakes in Jefferson County, Fon-du-Lac Reservoir ranks #7 for water quality.

Source: EPA Water Quality Portal sampling records, local state DNR records, last sampled 2024-09-21. Grade methodology: LakeGrade methodology.

Swimming Safety

Avoid swimming, very poor water quality, potential algae toxins

Water Quality Grade: F, Very Poor

Very murky, less than 1.3 ft of visibility. Phosphorus level: 81 µg/L. Chlorophyll-a: 40.7 µg/L. Trophic State Index: 69.

Metric	Value	Grade
Water Clarity (Secchi Depth)	1.3 ft	F
Phosphorus	81 µg/L	D
Chlorophyll-a (Algae)	40.7 µg/L	F
Trophic State Index (TSI)	69	Eutrophic

High nutrients, frequent algae, reduced clarity

Lake Details

Characteristic	Value
Surface Area	26 acres

Location

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County Ranking

Ranked #7 of 7 lakes in Jefferson County

Cleaner Lakes Within 30 Miles

Fon-du-Lac Reservoir holds Grade F. 5 nearby lakes hold higher grades.

See full comparison →

Nearby Lakes in Jefferson County

Lake Wauwanoka Nr. Dam

Lake Tishomingo Nr. Dam

Jefferson County

Cedar Hill Lake 1

Jefferson County

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Other Grade F Lakes in Wisconsin

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Jackson County · Clarity: 2 ft

Lake St. Louis by Dam

St. Charles County · Clarity: 2.3 ft

Hemitite Lake

St. Francois County · Clarity: 1.1 ft

Blind Pony Lake

Saline County · Clarity: 2.3 ft

Stockton Lake Upstream of Hwy 123 Bridge

Polk County · Clarity: 1.2 ft

Eutrophic Lakes in Wisconsin

Aspen Lake Along Southern Arm Boathouse Lake Hunnewell Lake Long Branch Lk. Lake

Reservoir Info (USACE NID)

Fon-du-Lac Reservoir is a man-made reservoir impounded by the Fondulac Dam (completed 1954), built primarily for recreation on the TR- SALINE CREEK; earth-type dam, 28 ft tall.

Surface area: 26 ac
Normal storage: 296 ac-ft
Max storage: 389 ac-ft
Drainage area: 346 sq mi
Hazard class: High
Owner: TRUSTEES-FON-DU-LAC SUBD

Source: USACE National Inventory of Dams, NID ID MO10699 · Operator website

Data Sources

Water quality data from the EPA Water Quality Portal

Grading methodology based on Metropolitan Council standards

Most recent sample: 2024-09-21

Monitoring stations: 1