Glenn Shoals Lake
Montgomery County, IllinoisView mapDirections
Illinois EPA publishes the water-quality measurements for Glenn Shoals Lake. Here is what has been measured.
- Hypereutrophic
- 63 ft max depth
- Public access
- Limited data
Glenn Shoals Lake in Montgomery County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Water clarity: 1 ft visibility. Phosphorus: 122 µg/L. Chlorophyll-a (algae): 72.1 µg/L.
Glenn Shoals Lake is a highly nutrient-loaded hypereutrophic lake in Montgomery County, Illinois with an estimated average depth of about 63 feet. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 1 other monitored lakes in Montgomery County, Glenn Shoals Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2022-11-01. Methodology: how these readings are compared.
What Glenn Shoals Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
Swimming conditions
Readings onlyLimited data
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Glenn Shoals Lake is safe to swim in today is a call for the Illinois Environmental Protection Agency and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Glenn Shoals Lake
These are the measurements Illinois EPA publishes for Glenn Shoals Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 1 ft of visibility. Phosphorus 122 µg/L. Chlorophyll-a 72.1 µg/L. TSI 74.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 122µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 72.1µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 74 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Glenn Shoals Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Glenn Shoals Lake typically sits around 61°F at the surface in October. Summer average is about 80°F. Usually warmest in Jul (about 85°F) and coldest in Nov (about 57°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (57°F) to its warmest (85°F).
Typical surface water temperature by month, from 77 field readings (2012–2022) via the EPA Water Quality Portal. See the full Glenn Shoals Lake water temperature breakdown →
Lake Details
Max depth
~63 ft est.
Public access
Yes
Listed by Illinois EPA
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Illinois has not published bathymetry for Glenn Shoals Lake.
Lake Size & Watershed
Watershed (drainage) area
73 sq mi
HydroLAKES / HydroSHEDS
Surface area
998 acres
HydroLAKES / HydroSHEDS
Shoreline
14.7 mi
HydroLAKES / HydroSHEDS
Elevation
594 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Recreation & Access
- Glenn Shoals LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Glenn Shoals Lake
Compare lakeside cabins, hotels, and vacation rentals near Glenn Shoals Lake in Montgomery 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 readings cover nutrients and algae, not lodging. Cabins and rentals around Glenn Shoals Lake are listed below.
Top-rated places to stay near Glenn Shoals Lake
Prices for Oct 23–25, 4 adults. Change dates on the map below.
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Planning a trip? Cabins and lodging at Glenn Shoals Lake → · more Illinois lake trips
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Fishing Glenn Shoals Lake
Reservoir Info (USACE NID)
Glenn Shoals Lake is a man-made reservoir impounded by the Lake Glenn Shoals Dam (completed 1978), built primarily for flood risk reduction on the MIDDLE FORK OF SHOAL CREEK; earth-type dam, 56 ft tall and 1,430 ft long.
- Normal storage
- 13,000 ac-ft
- Max storage
- 38,900 ac-ft
- Hazard class
- Significant
- Owner
- CITY OF HILLSBORO
All listed purposes: Flood Risk Reduction;Water Supply.
Source: USACE National Inventory of Dams, NID ID IL00971 · Operator website
Regulated Pollution Sources Nearby
4 EPA-permitted facilities operate within about 5 miles of Glenn Shoals Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 4 facilities have a reported Clean Water Act violation in the past three years.
- Hillsboro Stp, City OfHillsboro · 3.2 mi away · NPDES IL0029203MajorRecent violation
- Irving Stp, Village OfIrving · 3 mi away · NPDES IL0053881Recent violation
- Hillsboro Energy LlcHillsboro · 4.3 mi away · NPDES IL0080039Recent violation
- Hillsboro Energy LlcHillsboro · 4.4 mi away · NPDES IL0078727Recent violation
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.
Nearby Lakes in Montgomery County
Frequently asked questions about Glenn Shoals Lake
Where is Glenn Shoals Lake?
- Glenn Shoals Lake is a lake in Montgomery County, Illinois. Its water-quality measurements are published by Illinois EPA and shown on this page as reported.
What is the water quality of Glenn Shoals Lake?
- Glenn Shoals Lake in Montgomery County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Water clarity: 1 ft visibility. Phosphorus: 122 µg/L. Chlorophyll-a (algae): 72.1 µg/L.
Is Glenn Shoals Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Glenn Shoals Lake?
- Glenn Shoals Lake typically sits around 61°F at the surface in October, from 77 EPA Water Quality Portal field readings (2012–2022). That is a typical value for the month, not a live reading.
How deep is Glenn Shoals Lake?
- No published bathymetric survey covers Glenn Shoals Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 63 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Are there boat ramps on Glenn Shoals Lake?
- Glenn Shoals Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Glenn Shoals Lake. Public access is listed as yes.
Can I fish at Glenn Shoals Lake?
- Glenn Shoals Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Illinois's fish and wildlife agency, so check its current regulations before you go.
Explore Glenn Shoals Lake across LakeQuality
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Where this data comes from
48 measurements from 3 monitoring stations, 2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX48 samples · 2022
Analytical methods
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (3)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory