Clark Canyon Reservoir
Beaverhead County, Montana6,606 acresView mapDirections
Montana DEQ publishes the water-quality measurements for Clark Canyon Reservoir. Here is what has been measured.
- Mesotrophic
- Limited data
Clark Canyon Reservoir in Beaverhead County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Water clarity: 7.4 ft visibility. Phosphorus: 31 µg/L. Chlorophyll-a (algae): 5.2 µg/L. Surface area: 6606 acres.
Clark Canyon Reservoir is a 6,606-acre mesotrophic lake in Beaverhead County, Montana. Overall water quality is declining over recent sampling years. Compared to the 1 other monitored lakes in Beaverhead County, Clark Canyon Reservoir ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Montana DEQ, last sampled 2018-10-11. Methodology: how these readings are compared.
At about 6,600 acres, Clark Canyon Reservoir is large enough that where you stay decides which shore you see most of. If you are planning to stay, you can search lake houses and cabins around Clark Canyon Reservoir on Vrbo, or look for a hotel room near the lake on Booking.com or Expedia.
What Clark Canyon Reservoir is good for
From access and monitoring records, not editorial picks.
- Big water6,606 acres
Swimming conditions
Readings onlyLimited data
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Clark Canyon Reservoir is safe to swim in today is a call for the Montana Department of Environmental Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Clark Canyon Reservoir
These are the measurements Montana DEQ publishes for Clark Canyon Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Moderate clarity, visible to about 7.4 ft. Phosphorus 31 µg/L. Chlorophyll-a 5.2 µg/L. TSI 50.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 7.4ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 31µg/L | Fair GoodFairPoor |
| Chlorophyll-a (algae) | 5.2µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 50 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Clark Canyon Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
6,606 acres
No bathymetric survey has been published for Clark Canyon Reservoir, so its depth is not documented here.
Stays via Stay22
Stays near Clark Canyon Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Clark Canyon Reservoir in Beaverhead 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 Clark Canyon Reservoir
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Fishing Clark Canyon Reservoir
Water Quality Trend: Worsening
Based on 4 years of monitoring (2015–2018).
Water clarity
Worsening4 years
Phosphorus
Worsening+11.5 µg/L/yr2 years
Reservoir Info (USACE NID)
Clark Canyon Reservoir is a man-made reservoir impounded by the Clark Canyon Dam (completed 1964), built primarily for flood risk reduction on the Beaverhead River; earth-type dam, 148 ft tall and 2,950 ft long.
- Surface area
- 6,606 ac
- Normal storage
- 178,062 ac-ft
- Max storage
- 328,979 ac-ft
- Drainage area
- 2,321 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
All listed purposes: Flood Risk Reduction;Irrigation.
Source: USACE National Inventory of Dams, NID ID MT00569 · Operator website
Nearby Lakes in Beaverhead County
Frequently asked questions about Clark Canyon Reservoir
Where is Clark Canyon Reservoir?
- Clark Canyon Reservoir is a lake in Beaverhead County, Montana. Its water-quality measurements are published by Montana DEQ and shown on this page as reported.
What is the water quality of Clark Canyon Reservoir?
- Clark Canyon Reservoir in Beaverhead County, Montana has water-quality measurements published by Montana DEQ, shown here as reported. Water clarity: 7.4 ft visibility. Phosphorus: 31 µg/L. Chlorophyll-a (algae): 5.2 µg/L. Surface area: 6606 acres.
Is Clark Canyon Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Explore Clark Canyon Reservoir across LakeQuality
3 thermal springs within 11.6 mi, nearest McMenomey Ranch Spring
Species activity outlook by water temperature and season
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Where this data comes from
180 measurements from 9 monitoring stations, 2015–2018. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Montana DEQ WQPB
MDEQ_WQ_WQX180 samples · 2015–2018
Analytical methods
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (9)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.