Harmon Lake
Morton County, North Dakota144 acresView mapDirections
ND DEQ publishes the water-quality measurements for Harmon Lake. Here is what has been measured.
- Hypereutrophic
- Public access
- Limited data
Harmon Lake in Morton County, North Dakota has water-quality measurements published by ND DEQ, shown here as reported. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 48.5 µg/L. Surface area: 144 acres.
Harmon Lake is a 144-acre highly nutrient-loaded hypereutrophic lake in Morton County, North Dakota. 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. Methodology: how these readings are compared.
Harmon Lake covers about 140 acres in Morton County. It has one public boat landing. Vrbo is where to look for cabins and lake homes around Harmon Lake, and Booking.com and Expedia search hotels near the lake for your dates.
What Harmon Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
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. Check local advisories before you swim.
Whether Harmon Lake 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 Harmon Lake
These are the measurements ND DEQ publishes for Harmon Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 20 µg/L. Chlorophyll-a 48.5 µg/L. TSI 58.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 20µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 48.5µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 58 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Harmon Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Harmon Lake typically sits around 49°F at the surface in October. 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.
Column height runs from this lake’s coldest month (44°F) to its warmest (65°F).
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
Surface area
144 acres
Public access
Yes
Listed by ND DEQ
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
Stays via Stay22
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 readings cover nutrients and algae, not lodging. Cabins and rentals around Harmon Lake are listed below.
Top-rated places to stay near Harmon Lake
Prices for Oct 30–Nov 1, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip? Cabins and lodging at Harmon Lake → · more North Dakota lake trips
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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.
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. Its water-quality measurements are published by ND DEQ and shown on this page as reported.
What is the water quality of Harmon Lake?
- Harmon Lake in Morton County, North Dakota has water-quality measurements published by ND DEQ, shown here as reported. Phosphorus: 20 µg/L. Chlorophyll-a (algae): 48.5 µg/L. Surface area: 144 acres.
Is Harmon Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Harmon Lake?
- Harmon Lake typically sits around 49°F at the surface in October, 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.
Can I fish at Harmon Lake?
- Harmon Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. 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 Harmon Lake across LakeQuality
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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)
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
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