Stanley Reservoir is a 253-acre productive, nutrient-rich eutrophic lake in Mountrail County, North Dakota with a maximum depth of 23 feet (8-foot average). Water quality is graded D based on 2 sampling years through 2024. The lake supports 2 documented fish species including Rainbow Trout and Channel Catfish. Public access is available with 1 public boat landing. Compared to the 4 other monitored lakes in Mountrail County, Stanley Reservoir ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, North Dakota DNR, last sampled 2024-10-03. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Very murky, less than 1.1 ft of visibility. Chlorophyll-a: 19.5 µg/L. Trophic State Index: 68.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.1 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 19.5 µg/L | C |
| Trophic State Index (TSI) | 68 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 22.5 ft |
| Average Depth | 7.8 ft |
| Surface Area | 253 acres |
| Shoreline Length | 0.6 mi |
| Public Access | Yes |
Where to stay near Stanley Reservoir
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Fish Species
Click a species to see every graded lake where it is documented.
Fishing Stanley Reservoir
Recreation & Access
Location
County Ranking
Ranked #5 of 5 lakes in Mountrail County
Cleaner Lakes Within 30 Miles
Stanley Reservoir holds Grade D. 4 nearby lakes hold higher grades.
- CClearwater LakeMountrail County · 9.3 mi · Higher grade (D → C)
- CWhite Earth Dam LakeMountrail County · 19.6 mi · Higher grade (D → C)
- CPowers LakeMountrail County · 19.7 mi · Higher grade (D → C)
- CPowers Lake Dredge SiteMountrail County · 19.7 mi · Higher grade (D → C)
Nearby Lakes in Mountrail County
Explore Stanley Reservoir across LakeGrade
Fish species and top-graded lakes across North Dakota
Fish species and best lakes in Mountrail 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 D Lakes in North Dakota
Williams County · Clarity: 2.2 ft
Ward County · Clarity: 5.8 ft
Williams County · Clarity: 4.9 ft
Stark County · Clarity: 5.3 ft
Oliver County · Clarity: 1.3 ft
Hettinger County · Clarity: 3.8 ft
Eutrophic Lakes in North Dakota
More records, surveys & data sources
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
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: 2024-10-03
Monitoring stations: 1