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LakeQuality
D

Mermet Lake

Massac County, WisconsinEutrophic

Mermet Lake is a 1-acre productive, nutrient-rich eutrophic lake in Massac County, IL. Water quality is graded D based on 2 sampling years through 2021.

Source: EPA Water Quality Portal sampling records, local state DNR records, last sampled 2021-10-18. Grade methodology: LakeGrade methodology.

Swimming Safety

Swimming not recommended, poor water quality with high algae risk

Water Quality Grade: D, Poor

Very murky, less than 1.6 ft of visibility. Phosphorus level: 72 µg/L. Trophic State Index: 68.

MetricValueGrade
Water Clarity (Secchi Depth)1.6 ftF
Phosphorus72 µg/LD
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)68Eutrophic

High nutrients, frequent algae, reduced clarity

Lake Details

CharacteristicValue
Surface Area0.7 acres

Location

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County Ranking

Ranked #1 of 1 lakes in Massac County

Cleaner Lakes Within 30 Miles

Mermet Lake holds Grade D. 5 nearby lakes hold higher grades.

See full comparison →

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Other Grade D Lakes in Wisconsin

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Cook County · Clarity: 4.5 ft

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Cook County · Clarity: 4.5 ft

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Eutrophic Lakes in Wisconsin

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Reservoir Info (USACE NID)

Mermet Lake is a man-made reservoir impounded by the Mermet Dam (completed 1950), built primarily for recreation on the TRIB TUCKER DITCH; earth-type dam, 10 ft tall and 20,000 ft long.

Surface area
0.7 ac
Normal storage
904 ac-ft
Max storage
2,800 ac-ft
Drainage area
0.96 sq mi
Hazard class
Low
Owner
ILLINOIS DEPARTMENT OF NATURAL RESOURCES

Source: USACE National Inventory of Dams, NID ID IL50071 · Operator website

EPA Impairment Status

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

Causes of impairment

Nutrients (phosphorus, nitrogen)

Source: EPA ATTAINS assessment unit IL_RAB · 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: 2021-10-18

Monitoring stations: 3