What is the water quality grade for Mauvaise Terre Lake?

Mauvaise Terre Lake in Morgan County, Wisconsin received a water quality grade of F (Very Poor). Phosphorus: 162 µg/L. Surface area: 262 acres.

Is Mauvaise Terre Lake safe to swim in?

Avoid swimming, very poor water quality, potential algae toxins. Mauvaise Terre Lake has an overall water quality grade of F. Always check local health department advisories before swimming.

Mauvaise Terre Lake

Morgan County, WisconsinLimited DataHypereutrophic

Mauvaise Terre Lake is a 262-acre highly nutrient-loaded hypereutrophic lake in Morgan County, IL. Water quality is graded F based on 1 sampling years through 2021. Compared to the 1 other monitored lakes in Morgan County, Mauvaise Terre Lake ranks #2 for water quality.

Source: EPA Water Quality Portal sampling records, local state DNR records, last sampled 2021-10-04. Grade methodology: LakeGrade methodology.

Swimming Safety

Avoid swimming, very poor water quality, potential algae toxins

Water Quality Grade: F, Very Poor

No clarity data. Phosphorus level: 162 µg/L. Trophic State Index: 78.

Metric	Value	Grade
Water Clarity (Secchi Depth)	No data
Phosphorus	162 µg/L	F
Chlorophyll-a (Algae)	No data
Trophic State Index (TSI)	78	Hypereutrophic

Very high nutrients, dense algae, poor clarity

Lake Details

Characteristic	Value
Surface Area	262 acres

Location

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County Ranking

Ranked #2 of 2 lakes in Morgan County

Cleaner Lakes Within 30 Miles

Mauvaise Terre Lake holds Grade F. 2 nearby lakes hold higher grades.

See full comparison →

Nearby Lakes in Morgan County

More Wisconsin Lake Rankings

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Top 25 by overall water quality score

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Grade A/B + low algae filter

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Panfish-rich, public access

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Other Grade F Lakes in Wisconsin

Lake Charlemagne

Cook County · Clarity: 2 ft

Bode Lake North

Cook County · Clarity: 1.5 ft

Great Lakes Quarries West

Cook County · Clarity: 2.5 ft

Bull Frog Lake

Cook County · Clarity: 3 ft

Belly Deep Slough Lake

Cook County · Clarity: 0.7 ft

Sauk Lake

Cook County · Clarity: 1 ft

Hypereutrophic Lakes in Wisconsin

Bode Lake North Belly Deep Slough Lake Sauk Lake Washington Park Lagoon Lake

Reservoir Info (USACE NID)

Mauvaise Terre Lake is a man-made reservoir impounded by the Mauvaise Terre Lake Dam (completed 1923), built primarily for recreation on the MAUVAISE TERRE CREEK; earth-type dam, 30 ft tall and 850 ft long.

Surface area: 262 ac
Normal storage: 628 ac-ft
Max storage: 5,624 ac-ft
Drainage area: 34.3 sq mi
Hazard class: High
Owner: CITY OF JACKSONVILLE

All listed purposes: Recreation;Water Supply.

Source: USACE National Inventory of Dams, NID ID IL00709 · Operator website

EPA Impairment Status

Mauvaise Terre Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).

Causes of impairment

MercuryMetals (other than mercury)Nutrients (phosphorus, nitrogen)Turbidity

A Total Maximum Daily Load (TMDL) plan has been approved.

Source: EPA ATTAINS assessment unit IL_SDL · Official waterbody report

Data Sources

Water quality data from the EPA Water Quality Portal

Impairment status from EPA ATTAINS 303(d) database

Grading methodology based on Metropolitan Council standards

Most recent sample: 2021-10-04

Monitoring stations: 1