Mermet Lake is a 1-acre productive, nutrient-rich eutrophic lake in Massac County, Illinois. Water quality is graded D based on 2 sampling years through 2021. Limited fish-species data available. Public access is available with 3 public boat landings.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2021-10-18. Grade methodology: LakeGrade methodology.
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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.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.6 ft | F |
| Phosphorus | 72 µg/L | D |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 68 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 1 acres |
| Public Access | Yes |
Where to stay near Mermet Lake
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Fishing Mermet Lake
Recreation & Access
Water Temperature
Mermet Lake averages about 83°F at the surface in summer, usually warmest in Jun (about 83°F) and coldest in Apr (about 62°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 101 field readings (2016–2021) via the EPA Water Quality Portal. See the full Mermet Lake water temperature breakdown →
Location
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.
- BGlendale LakePope County · 14.7 mi · Two grade letters higher (D → B)
- BOne Horse Gap LakePope County · 28.2 mi · Two grade letters higher (D → B)
- CVienna Correctional Center LakeJohnson County · 11.5 mi · Higher grade (D → C)
- CLake of EgyptWilliamson County · 24.1 mi · Higher grade (D → C)
- DDutchman LakeJohnson County · 16.8 mi · Higher overall water quality score
Nearby Lakes in Massac County
Explore Mermet Lake across LakeGrade
More Illinois Lake Rankings
Other Grade D Lakes in Illinois
Eutrophic Lakes in Illinois
More records, surveys & data sources
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
Source: EPA ATTAINS assessment unit IL_RAB · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
5 EPA-permitted facilities operate within about 5 miles of Mermet Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 2 facilities have a reported Clean Water Act violation in the past three years.
- Electric Energy IncJoppa · 3.3 mi away · NPDES IL0004171MajorRecent violation
- Lafarge Midwest IncJoppa · 3.6 mi away · NPDES IL0004081Recent violation
- Trunkline Gas CompanyVarious · 2.6 mi away · NPDES IL0075876
- Met-South IncJoppa · 2.6 mi away · NPDES IL0078751
- 100-2 Conversion ProjectMassac, Johnson, And Wayne Counties · 3.4 mi away · NPDES IL0080089
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2021-10-18
Monitoring stations: 3