Hawthorn Lake
Mahaska County, WisconsinEutrophic
Hawthorn Lake is a 160-acre productive, nutrient-rich eutrophic lake in Mahaska County, IA. Water quality is graded D based on 2 sampling years through 2024. Compared to the 2 other monitored lakes in Mahaska County, Hawthorn Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, local state DNR records, last sampled 2024-08-28. Grade methodology: LakeGrade methodology.
Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Very murky, less than 2.4 ft of visibility. Chlorophyll-a: 27.5 µg/L. Trophic State Index: 64.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.4 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 27.5 µg/L | D |
| Trophic State Index (TSI) | 64 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 160 acres |
Location
County Ranking
Ranked #1 of 3 lakes in Mahaska County
Cleaner Lakes Within 30 Miles
Hawthorn Lake holds Grade D. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Mahaska County
More Wisconsin Lake Rankings
Other Grade D Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
Reservoir Info (USACE NID)
Hawthorn Lake is a man-made reservoir impounded by the Hawthorne Lake Dam (completed 1979), built primarily for recreation on the PLEASANT CREEK; earth-type dam, 45 ft tall and 900 ft long.
- Surface area
- 160 ac
- Normal storage
- 1,890 ac-ft
- Max storage
- 4,100 ac-ft
- Drainage area
- 5.2 sq mi
- Hazard class
- Significant
- Owner
- Iowa Department of Natural Resources
Source: USACE National Inventory of Dams, NID ID IA01874 · Operator website · Matched by proximity (0.14 km)
EPA Impairment Status
Hawthorn 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 IA 03-NSK-862 · 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: 2024-08-28
Monitoring stations: 1