Upper Stillwater Lake
Flathead County, MontanaView mapDirections
Not Rated: one monitoring station are on record, but they measured water clarity only. LakeQuality’s A–F method grades total phosphorus, total nitrogen, chlorophyll-a, and turbidity; clarity is shown, not scored.
- Limited data
Upper Stillwater Lake in Flathead County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 21.9 ft visibility.
- Clarity
- 21.9 ft
- Trend
- ↓ Declining
Stays via Stay22
Stays near Upper Stillwater Lake
Compare lakeside cabins, hotels, and vacation rentals near Upper Stillwater Lake in Flathead 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 Upper Stillwater Lake
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Watch Upper Stillwater Lake’s letter
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Why Upper Stillwater Lake has no grade
Upper Stillwater Lake has monitoring on record from one station, but only water clarity was measured. LakeQuality’s A–F letter uses total phosphorus, total nitrogen, chlorophyll-a, and turbidity against EPA National Lakes Assessment condition classes. With none of those grading measurements on record, Upper Stillwater Lake is Not Rated — not an F. Its 21.9-foot median from 6 readings collected 2020–2023 is still shown as clarity, but clarity alone cannot earn a letter.
Not Rated is EPA Integrated Reporting Category 3 — insufficient information. Everything below that has been measured is still reported on this page.
Sampling is run by Montana DEQ and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Upper Stillwater Lake is a lake in Flathead County, Montana. Overall water quality is declining over recent sampling years.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2023-08-27. Grade methodology: LakeQuality methodology.
What Upper Stillwater Lake is good for
From access and monitoring records, not editorial picks.
- Clear water21.9 ft of visibility
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Check local advisories before you swim.
Water quality measurements for Upper Stillwater Lake
These readings exist but are not enough for an A–F grade — see why.
Crystal clear, you can see 21.9 ft down. TSI 33.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 21.9 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 33 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Fishing Upper Stillwater Lake
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.357 m/yr | 2 |
Graded lakes near Upper Stillwater Lake
Upper Stillwater Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Flathead County
Frequently asked questions about Upper Stillwater Lake
Where is Upper Stillwater Lake?
- Upper Stillwater Lake is a lake in Flathead County, Montana. LakeQuality has not rated this lake (UNRATED) — the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity.
What is the water quality grade for Upper Stillwater Lake?
- Upper Stillwater Lake in Flathead County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 21.9 ft visibility.
Is Upper Stillwater Lake safe to swim in?
- The letter is not a swimming clearance. Check local advisories before you swim.
Explore Upper Stillwater Lake across LakeQuality
Planning a trip around Glacier?
Upper Stillwater Lake is about 39 miles from Glacier National Park. Crowds there swing hard by season, so the month you pick changes both how busy the park is and what lodging costs.
Best time to visit Glacier →More Montana Lake Rankings
Other Lakes in Montana
Oligotrophic Lakes in Montana
Where this data comes from
6 measurements from 1 monitoring station, 2020–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- North American Lake Management Society
NALMS6 samples · 2020–2023
Monitoring station identifiers (1)
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.