Stanley Reservoir
Mountrail County, North Dakota253 acresView mapDirections
ND DEQ publishes the water-quality measurements for Stanley Reservoir. Here is what has been measured.
- Hypereutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- 8 ft max depth
- Public access
- Limited data
Stanley Reservoir in Mountrail County, North Dakota has water-quality measurements published by ND DEQ, shown here as reported. Water clarity: 1.1 ft visibility. Phosphorus: 395 µg/L. Chlorophyll-a (algae): 19.5 µg/L. Surface area: 253 acres.
Stanley Reservoir is a 253-acre highly nutrient-loaded hypereutrophic lake in Mountrail County, North Dakota with an estimated average depth of about 8 feet. Limited fish-species data available. Public access is available. Compared to the 4 other monitored lakes in Mountrail County, Stanley Reservoir ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, NDDEQ, last sampled 2024-10-03. Methodology: how these readings are compared.
Swimming conditions
Readings onlyLimited data
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. Stanley Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Stanley Reservoir 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 Stanley Reservoir
These are the measurements ND DEQ publishes for Stanley Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 1.1 ft of visibility. Phosphorus 395 µg/L. Chlorophyll-a 19.5 µg/L. TSI 75.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1.1ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 395µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 19.5µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 75 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Stanley Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~8 ft est.
Surface area
253 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 Stanley Reservoir.
Lake Size & Watershed
Watershed (drainage) area
49 sq mi
HydroLAKES / HydroSHEDS
Shoreline
2.7 mi
HydroLAKES / HydroSHEDS
Elevation
2,146 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.
Stays via Stay22
Stays near Stanley Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Stanley Reservoir in Mountrail 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. The water-quality readings cover nutrients and algae, not lodging. Cabins and rentals around Stanley Reservoir are listed below.
Top-rated places to stay near Stanley Reservoir
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Fishing Stanley Reservoir
Reservoir Info (USACE NID)
Stanley Reservoir is a man-made reservoir impounded by the Stanley Dam (completed 1968), built primarily for water supply on the Little Knife River; earth-type dam, 21 ft tall and 860 ft long.
- Surface area
- 253 ac
- Normal storage
- 1,550 ac-ft
- Max storage
- 3,720 ac-ft
- Drainage area
- 22 sq mi
- Hazard class
- Low
- Owner
- City of Stanley
Source: USACE National Inventory of Dams, NID ID ND00192 · Operator website
EPA Impairment Status
Stanley Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit ND-10110101-009-L_00 · Official waterbody report
Nearby Lakes in Mountrail County
Frequently asked questions about Stanley Reservoir
Where is Stanley Reservoir?
- Stanley Reservoir is a lake in Mountrail 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 Stanley Reservoir?
- Stanley Reservoir in Mountrail County, North Dakota has water-quality measurements published by ND DEQ, shown here as reported. Water clarity: 1.1 ft visibility. Phosphorus: 395 µg/L. Chlorophyll-a (algae): 19.5 µg/L. Surface area: 253 acres.
Is Stanley Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Stanley Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
How deep is Stanley Reservoir?
- No published bathymetric survey covers Stanley Reservoir, 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 253 acres.
Can I fish at Stanley Reservoir?
- Public access to Stanley Reservoir is listed as yes on the lake record. 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 Stanley Reservoir across LakeQuality
Depth, room, public access, and the state wake-sport rules
Species activity outlook by water temperature and season
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Where this data comes from
24 measurements from 1 monitoring station, 2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North Dakota Department Of Environmental Quality
21NDHDWQ_WQX24 samples · 2024
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