Glenn Shoals Lake
Montgomery County, WisconsinHypereutrophic
Glenn Shoals Lake is a highly nutrient-loaded hypereutrophic lake in Montgomery County, IL. Water quality is graded F based on 2 sampling years through 2022. 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, local state DNR records, last sampled 2022-11-01. Grade methodology: LakeGrade methodology.
Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 1 ft of visibility. Phosphorus level: 91 µg/L. Trophic State Index: 73.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1 ft | F |
| Phosphorus | 91 µg/L | F |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 73 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Location
County Ranking
Ranked #1 of 2 lakes in Montgomery County
Cleaner Lakes Within 30 Miles
Glenn Shoals Lake holds Grade F. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Montgomery County
More Wisconsin Lake Rankings
Other Grade F Lakes in Wisconsin
Hypereutrophic Lakes in Wisconsin
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
EPA Impairment Status
Glenn Shoals 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_ROL · Official waterbody report
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Grading methodology based on Metropolitan Council standards
Most recent sample: 2022-11-01
Monitoring stations: 3