Deep Mill Lake
Yellowstone County, MontanaView mapDirections
Montana DEQ publishes the water-quality measurements for Deep Mill Lake. Here is what has been measured.
- Mesotrophic
- Limited data
Deep Mill Lake in Yellowstone County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 20 µg/L.
Deep Mill Lake is a mesotrophic lake in Yellowstone County, Montana.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2025-09-17. Methodology: how these readings are compared.
What Deep Mill Lake is good for
From access and monitoring records, not editorial picks.
- Camping1 public campground nearby
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 Deep Mill 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 Deep Mill Lake
These are the measurements Montana DEQ publishes for Deep Mill 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. TSI 47.
| 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) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 47 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Deep Mill Lake
Answers come straight from the public measurements and survey records on this page.
Recreation & Access
Public campgrounds near Deep Mill Lake
- Billings KOA Holiday4.7 km
Nearest public campgrounds in the USGS National Map inventory, within about 3 miles. An empty list means USGS records no campground that close, which is not the same as camping being unavailable. Where the source gives an official reservation link, it is used; the cabin and hotel search does not cover campsites. More camping lakes
Stays via Stay22
Stays near Deep Mill Lake
Compare lakeside cabins, hotels, and vacation rentals near Deep Mill Lake in Yellowstone 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.
Top-rated places to stay near Deep Mill 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 →
Follow Deep Mill Lake’s readings
Email me when new measurements post for this lake. Updates stay free.
Or email
Fishing Deep Mill Lake
Nearby Lakes in Yellowstone County
Frequently asked questions about Deep Mill Lake
Where is Deep Mill Lake?
- Deep Mill Lake is a lake in Yellowstone County, Montana. Its water-quality measurements are published by Montana DEQ and shown on this page as reported.
What is the water quality of Deep Mill Lake?
- Deep Mill Lake in Yellowstone County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Phosphorus: 20 µg/L.
Is Deep Mill Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Are there campgrounds on Deep Mill Lake?
- Deep Mill Lake has 1 public campground from USGS The National Map within 5 km, including Billings KOA Holiday. This is a location join, not a booking. Cabins and hotels are listed separately; campsite reservations use the official link when the source provides one.
Explore Deep Mill Lake across LakeQuality
More lakes in Montana
Other Lakes in Montana
Mesotrophic Lakes in Montana
Where this data comes from
6 measurements from 1 monitoring station, 2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Montana Volunteer Water Quality Monitoring
MTVOLWQM_WQX6 samples · 2025
Analytical methods
- Phosphorus by Colorimetry
- 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
Public campgrounds from USGS The National Map Structures, within about 3 miles