Lake Keomah
Mahaska County, WisconsinHypereutrophic
Lake Keomah is a 82-acre highly nutrient-loaded hypereutrophic lake in Mahaska County, IA. Water quality is graded F based on 2 sampling years through 2024. Compared to the 2 other monitored lakes in Mahaska County, Lake Keomah ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, local state DNR records, last sampled 2024-05-22. 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 1.5 ft of visibility. Chlorophyll-a: 63 µg/L. Trophic State Index: 71.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.5 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 63 µg/L | F |
| Trophic State Index (TSI) | 71 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 82 acres |
Location
County Ranking
Ranked #3 of 3 lakes in Mahaska County
Cleaner Lakes Within 30 Miles
Lake Keomah holds Grade F. 2 nearby lakes hold higher grades.
- BYenruogis PondKeokuk County · 18.4 mi · Two grade letters higher (F → B)
- DHawthorn LakeMahaska County · 13.2 mi · Higher grade (F → D)
Nearby Lakes in Mahaska County
More Wisconsin Lake Rankings
Other Grade F Lakes in Wisconsin
Hypereutrophic Lakes in Wisconsin
Reservoir Info (USACE NID)
Lake Keomah is a man-made reservoir impounded by the Lake Keomah Dam (completed 1935), built primarily for recreation on the TR-SOUTH SKUNK RIVER; earth-type dam, 42 ft tall and 1,100 ft long.
- Surface area
- 82 ac
- Normal storage
- 802 ac-ft
- Max storage
- 1,710 ac-ft
- Drainage area
- 3.1 sq mi
- Hazard class
- Significant
- Owner
- Iowa Department of Natural Resources
Source: USACE National Inventory of Dams, NID ID IA00642 · Operator website
EPA Impairment Status
Lake Keomah 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-SSK-930 · 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: 2024-05-22
Monitoring stations: 1