Loon Lake
Lake County, MontanaView mapDirections
Montana DEQ publishes the water-quality measurements for Loon Lake. Here is what has been measured.
- Mesotrophic
- 14 ft max depth
- Public access
Loon Lake in Lake County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 6.7 µg/L. Chlorophyll-a (algae): 2.2 µg/L.
Loon Lake is a mesotrophic lake in Lake County, Montana with an estimated average depth of about 14 feet. Overall water quality is declining over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings. Compared to the 17 other monitored lakes in Lake County, Loon Lake ranks #15 for water quality.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2023-08-02. Methodology: how these readings are compared.
Loon Lake has 2 public boat landings, so a lakefront rental is not the only way to get a boat on the water. Vrbo is where to look for cabins and lake homes around Loon Lake, and Booking.com and Expedia search hotels near the lake for your dates.
What Loon Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch2 documented ramps
Swimming conditions
Readings onlyElevated nutrients
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 Loon Lake is safe to swim in today is a call for the Montana Department of Environmental Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Loon Lake
These are the measurements Montana DEQ publishes for Loon 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 6.7 µg/L. Chlorophyll-a 2.2 µg/L. TSI 35.
| 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 | 6.7µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 2.2µg/L | Fair GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 35 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Loon Lake
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~14 ft est.
Public access
Yes
Listed by Montana DEQ
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Montana has not published bathymetry for Loon Lake.
Lake Size & Watershed
Watershed (drainage) area
4 sq mi
HydroLAKES / HydroSHEDS
Surface area
44 acres
HydroLAKES / HydroSHEDS
Shoreline
1.1 mi
HydroLAKES / HydroSHEDS
Elevation
3,081 ft
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Recreation & Access
- Horseshoe Lake/FerndalePublic
- Loon Lake/FerndalePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Loon Lake
Compare lakeside cabins, hotels, and vacation rentals near Loon Lake in Lake County, Montana — 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 Loon Lake are listed below.
Top-rated places to stay near Loon 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 whole trip? See where to stay at Montana’s top lakes →
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Fishing Loon Lake
Water Quality Trend: Worsening
Based on 11 years of monitoring (2012–2023).
Phosphorus
Worsening+1.39 µg/L/yr10 years
Chlorophyll-a
Worsening+0.57 µg/L/yr11 years
Nearby Lakes in Lake County
Frequently asked questions about Loon Lake
Where is Loon Lake?
- Loon Lake is a lake in Lake County, Montana. Its water-quality measurements are published by Montana DEQ and shown on this page as reported.
What is the water quality of Loon Lake?
- Loon Lake in Lake County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 6.7 µg/L. Chlorophyll-a (algae): 2.2 µg/L.
Is Loon Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
How deep is Loon Lake?
- No published bathymetric survey covers Loon Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 14 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Are there boat ramps on Loon Lake?
- Loon Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Horseshoe Lake/Ferndale, Loon Lake/Ferndale. Public access is listed as yes.
Can I fish at Loon Lake?
- Loon Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Montana's fish and wildlife agency, so check its current regulations before you go.
Explore Loon Lake across LakeQuality
More lakes in Montana
Other Lakes in Montana
Mesotrophic Lakes in Montana
Where this data comes from
24 measurements from 1 monitoring station, 2012–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Montana Watershed
MTWTRSHD_WQX24 samples · 2012–2023
Analytical methods
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 445.0 ~ EPA; Chlorophyll and Pheophytin in Algae by Fluorescence
- 4500 N C ~ Persufate Method for Total Nitrogen
Monitoring station identifiers (1)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory