Palmyra-Modesto Lake
Macoupin County, Illinois37 acresView mapDirections
Nutrients and algae run above the regional average.
↓ down from C at the last regrade
- Eutrophic
- Impaired · Algal growth
- #1 of 3 in the county
- Public access
- Limited data
Palmyra-Modesto Lake in Macoupin County, Illinois has a water quality grade of D (Nutrient-rich). Phosphorus: 60 µg/L. Chlorophyll-a (algae): 29.6 µg/L. Surface area: 37 acres.
- Typical in September
- 71°F
- Area
- 37 acres
- Type
- Eutrophic
- Phosphorus
- 60 µg/L
- Chlorophyll-a
- 29.6 µg/L
- Public access
- Yes
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Stays near Palmyra-Modesto Lake
Compare lakeside cabins, hotels, and vacation rentals near Palmyra-Modesto Lake in Macoupin County, Illinois — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Palmyra-Modesto Lake are listed below.
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Palmyra-Modesto Lake is a 37-acre productive, nutrient-rich eutrophic lake in Macoupin County, Illinois. Water quality is graded D based on 2 sampling years through 2021. Limited fish-species data available. Public access is available. 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 EPA, last sampled 2021-10-13. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The D is nutrients and algae, not a swimming clearance. Palmyra-Modesto Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, nutrients (phosphorus, nitrogen), pesticides, taste, color, odor, trash, turbidity. Check local advisories before you swim.
Water Quality Grade: D (Nutrient-rich)
No clarity data. Phosphorus 60 µg/L. Chlorophyll-a 29.6 µg/L. TSI 64. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 60 µg/L | Poor |
| Chlorophyll-a (Algae) | 29.6 µg/L | Poor |
| Trophic State Index (TSI) | 64 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Water Temperature
Palmyra-Modesto Lake typically sits around 71°F at the surface in September. Summer average is about 73°F. 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 →
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 37 acres |
| Public Access | Yes |
No bathymetric survey has been published for Palmyra-Modesto Lake, so its depth is not documented here.
Fishing Palmyra-Modesto Lake
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.
County Ranking
Ranked #1 of 3 lakes in Macoupin County
Nearby Lakes in Macoupin County
Frequently asked questions about Palmyra-Modesto Lake
Where is Palmyra-Modesto Lake?
- Palmyra-Modesto Lake is a lake in Macoupin County, Illinois. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Palmyra-Modesto Lake?
- Palmyra-Modesto Lake in Macoupin County, Illinois has a water quality grade of D (Nutrient-rich). Phosphorus: 60 µg/L. Chlorophyll-a (algae): 29.6 µg/L. Surface area: 37 acres.
Is Palmyra-Modesto Lake safe to swim in?
- The D is nutrients and algae, not a swimming clearance. Palmyra-Modesto Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, nutrients (phosphorus, nitrogen), pesticides, taste, color, odor, trash, turbidity. Check local advisories before you swim.
What is the water temperature of Palmyra-Modesto Lake?
- Palmyra-Modesto Lake typically sits around 71°F at the surface in September, from 263 EPA Water Quality Portal field readings (2011–2021). That is a typical value for the month, not a live reading.
Explore Palmyra-Modesto Lake across LakeQuality
More Illinois Lake Rankings
Other Grade D Lakes in Illinois
Eutrophic Lakes in Illinois
Where this data comes from
44 measurements from 2 monitoring stations, 2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX44 samples · 2021
Analytical methods
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (2)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)