Harmon Lake is a 144-acre productive, nutrient-rich eutrophic lake in Morton County, North Dakota with a maximum depth of 47 feet (16-foot average). Water quality is graded F based on 1 sampling years through 2023. The lake supports 6 documented fish species including Largemouth Bass, Bluegill, and Black Crappie. Public access is available with 1 public boat landing. Compared to the 3 other monitored lakes in Morton County, Harmon Lake ranks #4 for water quality.
Source: EPA Water Quality Portal sampling records, North Dakota DNR, last sampled 2023-07-12. Grade methodology: LakeGrade methodology.
Watch Harmon Lake water quality
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Swimming Safety
Avoid swimming, very poor water quality, potential algae toxins
Water Quality Grade: F, Very Poor
No clarity data. Chlorophyll-a: 48.5 µg/L. Trophic State Index: 69.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No data | |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 48.5 µg/L | F |
| Trophic State Index (TSI) | 69 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 46.8 ft |
| Average Depth | 16.1 ft |
| Surface Area | 144 acres |
| Shoreline Length | 4.8 mi |
| Public Access | Yes |
Where to stay near Harmon Lake
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Fish Species
Click a species to see every graded lake where it is documented.
Fishing Harmon Lake
Recreation & Access
Water Temperature
Harmon Lake averages about 63°F at the surface in summer, usually warmest in Aug (about 65°F) and coldest in Apr (about 44°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 86 field readings (2011–2023) via the EPA Water Quality Portal. See the full Harmon Lake water temperature breakdown →
Location
County Ranking
Ranked #4 of 4 lakes in Morton County
Cleaner Lakes Within 30 Miles
Harmon Lake holds Grade F. 5 nearby lakes hold higher grades.
- BArroda LakeOliver County · 23.9 mi · Two grade letters higher (F → B)
- CEast Arroda LakeOliver County · 23.9 mi · Two grade letters higher (F → C)
- DMcdowell Dam LakeBurleigh County · 17.4 mi · Higher grade (F → D)
- DNelson LakeOliver County · 14.5 mi · Higher grade (F → D)
- DNygren Dam LakeMorton County · 26.7 mi · Higher grade (F → D)
Nearby Lakes in Morton County
Explore Harmon Lake across LakeGrade
Fish species and top-graded lakes across North Dakota
Fish species and best lakes in Morton 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
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Other Grade F Lakes in North Dakota
Eutrophic Lakes in North Dakota
More records, surveys & data sources
Reservoir Info (USACE NID)
Harmon Lake is a man-made reservoir impounded by the Square Butte Creek Dam 6 (completed 2007), built primarily for recreation on the Otter Creek; earth-type dam, 81 ft tall and 2,100 ft long.
- Surface area
- 144 ac
- Normal storage
- 2,399 ac-ft
- Max storage
- 8,297 ac-ft
- Drainage area
- 37.4 sq mi
- Hazard class
- Significant
- Owner
- Morton County WRB
All listed purposes: Recreation;Flood Risk Reduction.
Source: USACE National Inventory of Dams, NID ID ND00794 · Operator website
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Harmon Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- South Central Regional Water District - Burleigh CountyBismarck · 3.5 mi away · NPDES ND0026301Recent violation
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
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: 2023-07-12
Monitoring stations: 3