Blacktail Dam Lake
Williams County, WisconsinEutrophic
Blacktail Dam Lake is a 158-acre productive, nutrient-rich eutrophic lake in Williams County, ND. Water quality is graded B based on 2 sampling years through 2025. Compared to the 8 other monitored lakes in Williams County, Blacktail Dam Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, local state DNR records, last sampled 2025-10-29. Grade methodology: LakeGrade methodology.
Swimming Safety
Good for swimming, clear water with low algae levels
Water Quality Grade: B, Good
Moderate clarity, visible to about 7.2 ft. Chlorophyll-a: 8.6 µg/L. Trophic State Index: 50.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 7.2 ft | C |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 8.6 µg/L | B |
| Trophic State Index (TSI) | 50 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 158 acres |
Location
County Ranking
Ranked #3 of 9 lakes in Williams County
Nearby Lakes in Williams County
More Wisconsin Lake Rankings
Other Grade B Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
Reservoir Info (USACE NID)
Blacktail Dam Lake is a man-made reservoir impounded by the Blacktail Dam (completed 1959), built primarily for recreation on the Blacktail Creek; earth-type dam, 63 ft tall and 2,250 ft long.
- Surface area
- 158 ac
- Normal storage
- 2,668.4 ac-ft
- Max storage
- 5,317.8 ac-ft
- Drainage area
- 27.7 sq mi
- Hazard class
- Significant
- Owner
- ND Game & Fish
All listed purposes: Recreation;Fish and Wildlife Pond.
Source: USACE National Inventory of Dams, NID ID ND00033 · Operator website
EPA Impairment Status
Blacktail Dam Lake is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit ND-10110102-003-L_00 · 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: 2025-10-29
Monitoring stations: 1