Mirror Lake is a 94-acre productive, nutrient-rich eutrophic lake in Adams County, North Dakota with a maximum depth of 16 feet (7-foot average). Water quality is graded F based on 2 sampling years through 2024. Overall water quality is declining over recent sampling years. The lake supports 6 documented fish species including Channel Catfish, Bluegill, and Northern Pike. Public access is available with 1 public boat landing. Compared to the 1 other monitored lakes in Adams County, Mirror Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, North Dakota DNR, last sampled 2024-09-24. Grade methodology: LakeGrade methodology.
Watch Mirror Lake water quality
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Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
Very murky, less than 2.1 ft of visibility. Chlorophyll-a: 31.6 µg/L. Trophic State Index: 65.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.1 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 31.6 µg/L | F |
| Trophic State Index (TSI) | 65 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 16.1 ft |
| Average Depth | 7.4 ft |
| Surface Area | 94 acres |
| Shoreline Length | 2.6 mi |
| Public Access | Yes |
Where to stay near Mirror Lake
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Fish Species
Click a species to see every graded lake where it is documented.
Fishing Mirror Lake
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.25 m/yr | 2 |
| Chlorophyll-a | ↓ Declining | +31 µg/L/yr | 2 |
Recreation & Access
Water Temperature
Mirror Lake averages about 59°F at the surface in summer, usually warmest in Jun (about 61°F) and coldest in Oct (about 47°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 23 field readings (2023–2023) via the EPA Water Quality Portal. See the full Mirror Lake water temperature breakdown →
Location
County Ranking
Ranked #2 of 2 lakes in Adams County
Cleaner Lakes Within 30 Miles
Mirror Lake holds Grade F. 5 nearby lakes hold higher grades.
- BNorth Lemmon LakeAdams County · 22.9 mi · Two grade letters higher (F → B)
- CIndian Creek Dam LakeHettinger County · 23.8 mi · Two grade letters higher (F → C)
- CBowman-Haley Dam LakeBowman County · 29.4 mi · Two grade letters higher (F → C)
- DGascoyne LakeBowman County · 23.9 mi · Higher grade (F → D)
- DCastle Rock Dam LakeHettinger County · 26.3 mi · Higher grade (F → D)
Nearby Lakes in Adams County
Explore Mirror Lake across LakeGrade
Fish species and top-graded lakes across North Dakota
Fish species and best lakes in Adams 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 F Lakes in North Dakota
Eutrophic Lakes in North Dakota
More records, surveys & data sources
Reservoir Info (USACE NID)
Mirror Lake is a man-made reservoir impounded by the Mirror Lake Dam (completed 1909), built primarily for recreation on the Flat Creek; earth-type dam, 19 ft tall and 800 ft long.
- Surface area
- 94.33 ac
- Normal storage
- 573 ac-ft
- Max storage
- 894.59 ac-ft
- Drainage area
- 0 sq mi
- Hazard class
- Significant
- Owner
- Hettinger Park Board
Source: USACE National Inventory of Dams, NID ID ND00137 · Operator website
EPA Impairment Status
Mirror 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-10130303-001-L_00 · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Mirror Lake under Clean Water Act (NPDES) discharge permits.
- Hettinger City OfHettinger · 1.9 mi away · NPDES ND0022497
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
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: 2024-09-24
Monitoring stations: 2