Arch Lake
Arch Lake in Carbon County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 50 acres.
- Area
- 50 acres
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Why Arch Lake has no grade
We grade a lake only when the monitoring record supports a letter: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Arch Lake, no water-quality sampling on record for this lake.
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. 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.
Arch Lake is a 50-acre lake in Carbon County, Montana.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled recent years. Grade methodology: LakeQuality methodology.
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Swimming Safety
Not ratedElevated nutrients
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Arch Lake
These readings exist but are not enough for an A–F grade — see why.
No clarity data. Trophic State Index: undefined.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) |
Where to stay near Arch Lake
Compare lakeside cabins, hotels, and vacation rentals near Arch Lake in Carbon 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 Arch Lake
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 50 acres |
No bathymetric survey has been published for Arch Lake, so its depth is not documented here.
Fishing Arch Lake
Nearby Lakes in Carbon County
Frequently asked questions about Arch Lake
Where is Arch Lake?
- Arch Lake is a lake in Carbon County, Montana. LakeQuality has not rated this lake (UNRATED) — no water-quality sampling on record for this lake.
What is the water quality grade for Arch Lake?
- Arch Lake in Carbon County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 50 acres.
Is Arch Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Arch Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
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Where this data comes from
Measurements for Arch Lake come from the EPA Water Quality Portal. Per-sample source details are not recorded for this lake.