Big Sag Lake
Big Sag Lake in Chouteau County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 149 acres.
- Area
- 149 acres
Next lake in Chouteau County
Swipe left or right on this bar to open the next or previous lake.
Why Big Sag 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 Big Sag 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.
Big Sag Lake is a 149-acre lake in Chouteau County, Montana.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled recent years. Grade methodology: LakeQuality methodology.
Watch Big Sag Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Not ratedElevated nutrients
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Big Sag 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 Big Sag Lake
Compare lakeside cabins, hotels, and vacation rentals near Big Sag Lake in Chouteau 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 Big Sag Lake
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 →
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 149 acres |
No bathymetric survey has been published for Big Sag Lake, so its depth is not documented here.
Fishing Big Sag Lake
Nearby Lakes in Chouteau County
Frequently asked questions about Big Sag Lake
Where is Big Sag Lake?
- Big Sag Lake is a lake in Chouteau 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 Big Sag Lake?
- Big Sag Lake in Chouteau County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 149 acres.
Is Big Sag Lake safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Big Sag Lake is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
Explore Big Sag Lake across LakeQuality
More Montana Lake Rankings
Other Lakes in Montana
Where this data comes from
Measurements for Big Sag Lake come from the EPA Water Quality Portal. Per-sample source details are not recorded for this lake.