Mattoon Lake is a 980-acre highly nutrient-loaded hypereutrophic lake in Cumberland County, Illinois. Water quality is graded F based on 2 sampling years through 2022. Limited fish-species data available. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2022-10-27. Grade methodology: LakeGrade methodology.
Watch Mattoon Lake water quality
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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: 206 µg/L. Trophic State Index: 77.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.3 ft | F |
| Phosphorus | 206 µg/L | F |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 77 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 980 acres |
| Public Access | Yes |
Where to stay near Mattoon Lake
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Fishing Mattoon Lake
Recreation & Access
Water Temperature
Mattoon Lake averages about 78°F at the surface in summer, usually warmest in Jul (about 82°F) and coldest in Apr (about 59°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 101 field readings (2012–2022) via the EPA Water Quality Portal. See the full Mattoon Lake water temperature breakdown →
Location
County Ranking
Ranked #1 of 1 lakes in Cumberland County
Cleaner Lakes Within 30 Miles
Mattoon Lake holds Grade F. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Cumberland County
Explore Mattoon Lake across LakeGrade
Species activity outlook by water temperature and season
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Very high nutrients, dense algae, poor clarity
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More records, surveys & data sources
Reservoir Info (USACE NID)
Mattoon Lake is a man-made reservoir impounded by the Lake Mattoon Dam (completed 1957), built primarily for recreation on the LITTLE WABASH RIVER; earth-type dam, 46 ft tall and 2,250 ft long.
- Surface area
- 980 ac
- Normal storage
- 11,820 ac-ft
- Max storage
- 22,569 ac-ft
- Drainage area
- 57 sq mi
- Hazard class
- Significant
- Owner
- CITY OF MATTOON
All listed purposes: Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID IL00141 · Operator website
EPA Impairment Status
Mattoon Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IL_RCF · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
4 EPA-permitted facilities operate within about 5 miles of Mattoon Lake under Clean Water Act (NPDES) discharge permits. 2 facilities have a reported Clean Water Act violation in the past three years.
- Rich Overzet Private Sewage Disposal SystemNeoga · 1.1 mi away · NPDES IL0080269Recent violation
- Neoga Stp, City OfNeoga · 2.2 mi away · NPDES IL0030091Recent violation
- David L. Paul Private Sewage Disposal SystemNeoga · 0.3 mi away · NPDES IL0080305
- Josh Denson Private Sewage Disposal SystemNeoga · 0.6 mi away · NPDES IL0080208
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: 2022-10-27
Monitoring stations: 5