Hannen Lake
Benton County, WisconsinHypereutrophic
Hannen Lake is a 39-acre highly nutrient-loaded hypereutrophic lake in Benton County, IA. Water quality is graded F based on 2 sampling years through 2024. Compared to the 1 other monitored lakes in Benton County, Hannen Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, local state DNR records, last sampled 2024-10-23. 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 1.2 ft of visibility. Chlorophyll-a: 119.9 µg/L. Trophic State Index: 76.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.2 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 119.9 µg/L | F |
| Trophic State Index (TSI) | 76 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 39 acres |
Location
County Ranking
Ranked #1 of 2 lakes in Benton County
Cleaner Lakes Within 30 Miles
Hannen Lake holds Grade F. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Benton County
More Wisconsin Lake Rankings
Other Grade F Lakes in Wisconsin
Hypereutrophic Lakes in Wisconsin
Reservoir Info (USACE NID)
Hannen Lake is a man-made reservoir impounded by the Hannen Lake Dam (completed 1959), built primarily for recreation on the TR-COON CREEK; earth-type dam, 35 ft tall and 600 ft long.
- Surface area
- 39 ac
- Normal storage
- 390 ac-ft
- Max storage
- 886 ac-ft
- Drainage area
- 0.96 sq mi
- Hazard class
- Significant
- Owner
- Benton County Conservation Board
Source: USACE National Inventory of Dams, NID ID IA00128 · Operator website
EPA Impairment Status
Hannen Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IA 02-IOW-704 · 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: 2024-10-23
Monitoring stations: 1