East Bay Lake
Lake County, MontanaView mapDirections
Clarity, phosphorus, and algae sit in the clean band for this region.
↓ down from A at the last regrade
- Oligotrophic
- #8 of 18 in the county
East Bay Lake in Lake County, Montana has a water quality grade of B (Good). Phosphorus: 3 µg/L.
- Type
- Oligotrophic
- Phosphorus
- 3 µg/L
- Trend
- ↓ Declining
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Stays near East Bay Lake
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Watch East Bay Lake’s letter
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East Bay Lake is a cold, clear oligotrophic lake in Lake County, Montana. Water quality is graded B based on 2 sampling years through 2026. Overall water quality is declining over recent sampling years. Compared to the 17 other monitored lakes in Lake County, East Bay Lake ranks #8 for water quality.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2026-06-30. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLow algae
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The B is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: B (Good)
No clarity data. Phosphorus 3 µg/L. TSI 20. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 3 µg/L | Good |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 20 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
Fishing East Bay Lake
Water Quality Trend: ↓ Declining
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↓ Declining | +1.5 µg/L/yr | 3 |
County Ranking
Ranked #8 of 18 lakes in Lake County
Nearby Lakes in Lake County
Frequently asked questions about East Bay Lake
Where is East Bay Lake?
- East Bay Lake is a lake in Lake County, Montana. LakeQuality grades it B for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for East Bay Lake?
- East Bay Lake in Lake County, Montana has a water quality grade of B (Good). Phosphorus: 3 µg/L.
Is East Bay Lake safe to swim in?
- The B is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Explore East Bay Lake across LakeQuality
Species activity outlook by water temperature and season
Where to stay at Montana's top lakes, each with its grade
Low nutrients, clear water. The letter is not a swimming clearance.
Montana's cleanest and most-polluted lakes, ranked
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Other Grade B Lakes in Montana
Oligotrophic Lakes in Montana
Where this data comes from
52 measurements from 1 monitoring station, 2023–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Confederated Salish and Kootenai Tribes
CSKTRIBE52 samples · 2023–2026
Analytical methods
- Phosphorus by Colorimetry
- 4500 N C ~ Persufate Method for Total Nitrogen
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.