Palmyra-Modesto Lake is a 37-acre productive, nutrient-rich eutrophic lake in Macoupin County, Illinois. Water quality is graded C based on 1 sampling years through 2021. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 2 other monitored lakes in Macoupin County, Palmyra-Modesto Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2021-10-13. Grade methodology: LakeGrade methodology.
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Swimming Safety
Generally safe for swimming, moderate water quality
Water Quality Grade: C, Fair
No clarity data. Phosphorus level: 56 µg/L. Trophic State Index: 62.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No data | |
| Phosphorus | 56 µg/L | C |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 62 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 37 acres |
| Public Access | Yes |
Where to stay near Palmyra-Modesto Lake
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Fishing Palmyra-Modesto Lake
Recreation & Access
Water Temperature
Palmyra-Modesto Lake averages about 73°F at the surface in summer, usually warmest in Aug (about 75°F) and coldest in Apr (about 52°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 263 field readings (2011–2021) via the EPA Water Quality Portal. See the full Palmyra-Modesto Lake water temperature breakdown →
Location
County Ranking
Ranked #1 of 3 lakes in Macoupin County
Nearby Lakes in Macoupin County
Explore Palmyra-Modesto Lake across LakeGrade
More Illinois Lake Rankings
Other Grade C Lakes in Illinois
Eutrophic Lakes in Illinois
More records, surveys & data sources
Reservoir Info (USACE NID)
Palmyra-Modesto Lake is a man-made reservoir impounded by the Palmyra-Modesto City Lake Dam (completed 1965), built primarily for water supply on the TRIB NASSA CREEK; earth-type dam, 50 ft tall and 620 ft long.
- Surface area
- 37 ac
- Normal storage
- 565 ac-ft
- Max storage
- 967 ac-ft
- Drainage area
- 1.8 sq mi
- Hazard class
- Significant
- Owner
- PALMYRA-MODESTO WATER COMMISSION
Source: USACE National Inventory of Dams, NID ID IL00772 · Operator website · Matched by proximity (0.29 km)
EPA Impairment Status
Palmyra-Modesto 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_RDZP · Official waterbody report
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Palmyra-Modesto Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Palmyra Stp, Village OfPalmyra · 3.1 mi away · NPDES IL0044831Recent violation
- Palmyra-Modesto Comm WtpPalmyra · 0.2 mi away · NPDES IL0044822
- Illini FeedersPalmyra · 1.6 mi away · NPDES IL0063436
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)
Grading methodology based on Metropolitan Council standards
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2021-10-13
Monitoring stations: 2