Blacktail Dam Lake
Williams County, North Dakota158 acresView mapDirections
ND DEQ publishes the water-quality measurements for Blacktail Dam Lake. Here is what has been measured.
- Eutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- 8 ft max depth
- Public access
Blacktail Dam Lake in Williams County, North Dakota has water-quality measurements published by ND DEQ, shown here as reported. Water clarity: 7.2 ft visibility. Phosphorus: 53 µg/L. Chlorophyll-a (algae): 8.6 µg/L. Surface area: 158 acres.
Blacktail Dam Lake is a 158-acre productive, nutrient-rich eutrophic lake in Williams County, North Dakota with an estimated average depth of about 8 feet. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 5 other monitored lakes in Williams County, Blacktail Dam Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, NDDEQ, last sampled 2025-10-29. Methodology: how these readings are compared.
Blacktail Dam Lake covers about 160 acres in Williams County. It has one public boat landing. If you are planning to stay, you can search lake houses and cabins around Blacktail Dam Lake on Vrbo, or look for a hotel room near the lake on Booking.com or Expedia.
What Blacktail Dam Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
Swimming conditions
Readings onlyModerate algae
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Blacktail Dam Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen), oxygen depletion (low DO). Check local advisories before you swim.
Whether Blacktail Dam Lake is safe to swim in today is a call for the North Dakota Department of Environmental Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Blacktail Dam Lake
These are the measurements ND DEQ publishes for Blacktail Dam Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Moderate clarity, visible to about 7.2 ft. Phosphorus 53 µg/L. Chlorophyll-a 8.6 µg/L. TSI 54.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 7.2ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 53µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 8.6µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 54 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Blacktail Dam Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Blacktail Dam Lake typically sits around 49°F at the surface in October. Summer average is about 62°F. Usually warmest in Jul (about 63°F) and coldest in Feb (about 38°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (38°F) to its warmest (63°F).
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 →
Lake Details
Max depth
~8 ft est.
Surface area
158 acres
Public access
Yes
Listed by ND DEQ
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. North Dakota has not published bathymetry for Blacktail Dam Lake.
Lake Size & Watershed
Watershed (drainage) area
29 sq mi
HydroLAKES / HydroSHEDS
Shoreline
2.1 mi
HydroLAKES / HydroSHEDS
Elevation
2,077 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Recreation & Access
- Blacktail DamPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Blacktail Dam Lake
Compare lakeside cabins, hotels, and vacation rentals near Blacktail Dam Lake in Williams County, North Dakota — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Blacktail Dam Lake
Prices for Oct 23–25, 4 adults. Change dates on the map below.
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Fishing Blacktail Dam Lake
Water Quality Trend: Improving
Based on 6 years of monitoring (2020–2025).
Water clarity
Worsening3 years
Phosphorus
Improving-6.25 µg/L/yr3 years
Chlorophyll-a
Improving-2.02 µg/L/yr5 years
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
Nearby Lakes in Williams County
Frequently asked questions about Blacktail Dam Lake
Where is Blacktail Dam Lake?
- Blacktail Dam Lake is a lake in Williams County, North Dakota. Its water-quality measurements are published by ND DEQ and shown on this page as reported.
What is the water quality of Blacktail Dam Lake?
- Blacktail Dam Lake in Williams County, North Dakota has water-quality measurements published by ND DEQ, shown here as reported. Water clarity: 7.2 ft visibility. Phosphorus: 53 µg/L. Chlorophyll-a (algae): 8.6 µg/L. Surface area: 158 acres.
Is Blacktail Dam Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Blacktail Dam Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen), oxygen depletion (low DO). Check local advisories before you swim.
What is the water temperature of Blacktail Dam Lake?
- Blacktail Dam Lake typically sits around 49°F at the surface in October, from 167 EPA Water Quality Portal field readings (2014–2025). That is a typical value for the month, not a live reading.
How deep is Blacktail Dam Lake?
- No published bathymetric survey covers Blacktail Dam Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 8 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 158 acres.
Are there boat ramps on Blacktail Dam Lake?
- Blacktail Dam Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Blacktail Dam. Public access is listed as yes.
Can I fish at Blacktail Dam Lake?
- Blacktail Dam Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by North Dakota's fish and wildlife agency, so check its current regulations before you go.
Explore Blacktail Dam Lake across LakeQuality
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Where this data comes from
165 measurements from 1 monitoring station, 2020–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North Dakota Department Of Environmental Quality
21NDHDWQ_WQX165 samples · 2020–2025
Analytical methods
- Phosphorus by Colorimetry
- 447.0 ~ EPA; Chlorophyll a and b in phytoplankton by HPLC/UV
- 4500 NO3 E ~ Nitrate in Water- Cadmium Reduction
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Depth, fish, and access data from North Dakota Game & Fish
Named boat-access points from the USGS National Boat Ramps inventory