Beaver 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.
- Impaired · Mercury
- Limited data
Beaver Lake in Flathead County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 18.8 ft visibility.
- Clarity
- 18.8 ft
- Trend
- ↓ Declining
Stays via Stay22
Stays near Beaver Lake
Compare lakeside cabins, hotels, and vacation rentals near Beaver 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 Beaver Lake
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Watch Beaver Lake’s letter
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Why Beaver Lake has no grade
Beaver 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, Beaver Lake is Not Rated — not an F. Its 18.8-foot median from 13 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.
Beaver 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 2023-09-18. Grade methodology: LakeQuality methodology.
What Beaver Lake is good for
From access and monitoring records, not editorial picks.
- Clear water18.8 ft of visibility
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Beaver Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, pCBs. Check local advisories before you swim.
Water quality measurements for Beaver Lake
These readings exist but are not enough for an A–F grade — see why.
Crystal clear, you can see 18.8 ft down. TSI 35.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 18.8 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 35 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Fishing Beaver Lake
Water Quality Trend: ↓ Declining
Based on 12 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.461 m/yr | 4 |
| Phosphorus | ↓ Declining | +1.17 µg/L/yr | 11 |
| Chlorophyll-a | ↑ Improving | -0.33 µg/L/yr | 12 |
EPA Impairment Status
Beaver Lake is officially listed as impaired under Clean Water Act §303(d) in the 2021 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit MT76P004_010 · Official waterbody report · Matched by proximity (2.94 km)
Graded lakes near Beaver Lake
Beaver Lake has no grade, but these lakes within a short drive do.
Nearby Lakes in Flathead County
Frequently asked questions about Beaver Lake
Where is Beaver Lake?
- Beaver 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 Beaver Lake?
- Beaver Lake in Flathead County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 18.8 ft visibility.
Is Beaver Lake safe to swim in?
- The letter is not a swimming clearance. Beaver Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, pCBs. Check local advisories before you swim.
Explore Beaver Lake across LakeQuality
Planning a trip around Glacier?
Beaver Lake is about 33 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
13 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
NALMS13 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.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database