Blacktail Dam Lake is a 158-acre productive, nutrient-rich eutrophic lake in Williams County, North Dakota with a maximum depth of 36 feet (15-foot average). Water quality is graded B based on 2 sampling years through 2025. Water clarity is declining over recent sampling years. The lake supports 5 documented fish species including Northern Pike, Walleye, and Bluegill. Public access is available with 1 public boat landing. 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, North Dakota DNR, last sampled 2025-10-29. Grade methodology: LakeGrade methodology.
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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 |
|---|---|
| Maximum Depth | 36.3 ft |
| Average Depth | 15.2 ft |
| Surface Area | 158 acres |
| Shoreline Length | 5.6 mi |
| Public Access | Yes |
Where to stay near Blacktail Dam Lake
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Fish Species
Click a species to see every graded lake where it is documented.
Fishing Blacktail Dam Lake
Water Quality Trend: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.375 m/yr | 3 |
| Chlorophyll-a | ↑ Improving | -2.02 µg/L/yr | 5 |
Recreation & Access
Water Temperature
Blacktail Dam Lake averages about 62°F at the surface in summer, usually warmest in Jul (about 63°F) and coldest in Feb (about 38°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 167 field readings (2014–2025) via the EPA Water Quality Portal. See the full Blacktail Dam Lake water temperature breakdown →
Location
County Ranking
Ranked #3 of 9 lakes in Williams County
Nearby Lakes in Williams County
Explore Blacktail Dam Lake across LakeGrade
Fish species and top-graded lakes across North Dakota
Fish species and best lakes in Williams County
Species activity outlook by water temperature and season
Where to stay at North Dakota's top lakes, each with its grade
High nutrients, frequent algae, reduced clarity
North Dakota's cleanest and most-polluted lakes, ranked
More North Dakota Lake Rankings
Other Grade B Lakes in North Dakota
Eutrophic Lakes in North Dakota
More records, surveys & data sources
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
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Depth, fish, and access data from North Dakota Game & Fish
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2025-10-29
Monitoring stations: 1