Harmon Lake
Morton County, North Dakota144 acresView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- #4 of 4 in the county
- Public access
- Limited data
Harmon Lake in Morton County, North Dakota has a water quality grade of F (Algae-prone). Phosphorus: 20 µg/L. Chlorophyll-a (algae): 48.5 µg/L. Surface area: 144 acres.
- Typical in September
- 57°F
- Area
- 144 acres
- Type
- Hypereutrophic
- Phosphorus
- 20 µg/L
- Chlorophyll-a
- 48.5 µg/L
- Public access
- Yes
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Stays near Harmon Lake
Compare lakeside cabins, hotels, and vacation rentals near Harmon Lake in Morton 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 grade measures nutrients and algae, not lodging — cabins and rentals around Harmon Lake are listed below.
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Harmon Lake is a 144-acre highly nutrient-loaded hypereutrophic lake in Morton County, North Dakota. Water quality is graded F based on 3 sampling years through 2023. Limited fish-species data available. 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, NDDEQ, last sampled 2023-07-12. Grade methodology: LakeQuality methodology.
What Harmon Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The F is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
No clarity data. Phosphorus 20 µg/L. Chlorophyll-a 48.5 µg/L. TSI 58. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 20 µg/L | Good |
| Chlorophyll-a (Algae) | 48.5 µg/L | Poor |
| Trophic State Index (TSI) | 58 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Harmon Lake typically sits around 57°F at the surface in September. Summer average is about 63°F. 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 →
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 144 acres |
| Public Access | Yes |
No bathymetric survey has been published for Harmon Lake, so its depth is not documented here.
Recreation & Access
- Harmon LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Harmon Lake
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.
County Ranking
Ranked #4 of 4 lakes in Morton County
Nearby Lakes With Higher Grades
Harmon Lake holds Grade F. One nearby lake has a higher nutrient-and-algae grade — useful for a swim day, not a reason to skip lodging here.
Nearby Lakes in Morton County
Frequently asked questions about Harmon Lake
Where is Harmon Lake?
- Harmon Lake is a lake in Morton County, North Dakota. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Harmon Lake?
- Harmon Lake in Morton County, North Dakota has a water quality grade of F (Algae-prone). Phosphorus: 20 µg/L. Chlorophyll-a (algae): 48.5 µg/L. Surface area: 144 acres.
Is Harmon Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Harmon Lake?
- Harmon Lake typically sits around 57°F at the surface in September, from 86 EPA Water Quality Portal field readings (2011–2023). That is a typical value for the month, not a live reading.
Are there boat ramps on Harmon Lake?
- Harmon Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Harmon Lake. Public access is listed as yes.
Explore Harmon Lake across LakeQuality
Species activity outlook by water temperature and season
Where to stay at North Dakota's top lakes, each with its grade
Very high nutrients, dense algae, poor clarity
North Dakota's cleanest and most-polluted lakes, ranked
More North Dakota Lake Rankings
Other Grade F Lakes in North Dakota
Hypereutrophic Lakes in North Dakota
Where this data comes from
15 measurements from 3 monitoring stations, 2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North Dakota Department Of Environmental Quality
21NDHDWQ_WQX15 samples · 2023
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 (3)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Depth, fish, and access data from North Dakota Game & Fish
Named boat-access points from the USGS National Boat Ramps inventory