Where is Thompson Falls Reservoir?

Thompson Falls Reservoir is a lake in Sanders County, Montana. LakeQuality has not rated this lake (UNRATED) — no water-quality sampling on record for this lake.

Is Thompson Falls Reservoir safe to swim in?

Not rated for swimming — there is not enough monitoring data to judge this lake. Thompson Falls Reservoir is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.

Are there boat ramps on Thompson Falls Reservoir?

Thompson Falls Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Thompson Falls. Public access is listed as yes.

Thompson Falls Reservoir

Not yet rated

211 acres

Thompson Falls Reservoir in Sanders County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 211 acres.

Area: 211 acres
Public access: Yes

Where to stay →Safe to swim?

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Why Thompson Falls Reservoir 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 Thompson Falls Reservoir, 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.

Thompson Falls Reservoir is a 211-acre lake in Sanders County, Montana. Limited fish-species data available. Public access is available with 1 public boat landing.

Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled recent years. Grade methodology: LakeQuality methodology.

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Swimming Safety

Not rated

Elevated nutrients

Not rated for swimming — there is not enough monitoring data to judge this lake

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Water quality measurements for Thompson Falls Reservoir

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 Thompson Falls Reservoir

Compare lakeside cabins, hotels, and vacation rentals near Thompson Falls Reservoir in Sanders 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 Thompson Falls Reservoir

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Lake Details

Characteristic	Value
Surface Area	211 acres
Public Access	Yes

No bathymetric survey has been published for Thompson Falls Reservoir, so its depth is not documented here.

Recreation & Access

Boat Landings

Yes

Public Access

Thompson FallsPublic

Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps

Fishing Thompson Falls Reservoir

→ Thompson Falls Reservoir fishing regulations (limits, seasons, special rules)

Nearby Lakes in Sanders County

NRNoxon ReservoirView →NRFishtrap LakeView →NRWanless LakeView →NRLower Thompson LakeView →NRRock LakeView →NRRainbow LakeView →

Frequently asked questions about Thompson Falls Reservoir

Where is Thompson Falls Reservoir?: Thompson Falls Reservoir is a lake in Sanders 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 Thompson Falls Reservoir?: Thompson Falls Reservoir in Sanders County, Montana is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 211 acres.
Is Thompson Falls Reservoir safe to swim in?: Not rated for swimming — there is not enough monitoring data to judge this lake. Thompson Falls Reservoir is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
Are there boat ramps on Thompson Falls Reservoir?: Thompson Falls Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Thompson Falls. Public access is listed as yes.