Deadwood Reservoir
Valley County, Idaho3,800 acresView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
- Oligotrophic
- #2 of 9 in the county
- Limited data
Deadwood Reservoir in Valley County, Idaho has a water quality grade of A (Excellent). Water clarity: 17.2 ft visibility. Phosphorus: 14 µg/L. Chlorophyll-a (algae): 1.7 µg/L. Surface area: 3800 acres.
- Clarity
- 17.2 ft
- Area
- 3,800 acres
- Type
- Oligotrophic
- Phosphorus
- 14 µg/L
- Chlorophyll-a
- 1.7 µg/L
- Trend
- → Stable
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Watch Deadwood Reservoir’s letter
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Deadwood Reservoir is a 3,800-acre cold, clear oligotrophic lake in Valley County, Idaho. Water quality is graded A based on 2 sampling years through 2021. Water clarity is declining over recent sampling years. Compared to the 8 other monitored lakes in Valley County, Deadwood Reservoir ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, IDEQ, last sampled 2021-08-04. Grade methodology: LakeQuality methodology.
What Deadwood Reservoir is good for
From access and monitoring records, not editorial picks.
- Clear water17.2 ft of visibility
- Big water3,800 acres
Swimming Safety
Grade onlyLimited data
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 A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: A (Excellent)
Crystal clear, you can see 17.2 ft down. Phosphorus 14 µg/L. Chlorophyll-a 1.7 µg/L. TSI 38. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 17.2 ft | Not graded |
| Phosphorus | 14 µg/L | Good |
| Chlorophyll-a (Algae) | 1.7 µg/L | Good |
| Trophic State Index (TSI) | 38 | Oligotrophic |
Low nutrients, clear water. The letter is not a swimming clearance.
→ Deadwood Reservoir water level: the live USGS gauge reading
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 3,800 acres |
No bathymetric survey has been published for Deadwood Reservoir, so its depth is not documented here.
Fishing Deadwood Reservoir
Water Quality Trend: → Stable
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.191 m/yr | 6 |
| Phosphorus | → Stable | -0.08 µg/L/yr | 3 |
| Chlorophyll-a | ↑ Improving | -0.09 µg/L/yr | 6 |
Reservoir Info (USACE NID)
Deadwood Reservoir is a man-made reservoir impounded by the Deadwood Dam (completed 1931), built primarily for hydroelectric on the Deadwood River South Fork Payette River; concrete-type dam, 165 ft tall and 749 ft long.
- Surface area
- 3,800 ac
- Max storage
- 153,992 ac-ft
- Drainage area
- 109.43 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
All listed purposes: Hydroelectric;Irrigation;Recreation.
Source: USACE National Inventory of Dams, NID ID ID00284 · Operator website
County Ranking
Ranked #2 of 9 lakes in Valley County
Nearby Lakes in Valley County
Frequently asked questions about Deadwood Reservoir
Where is Deadwood Reservoir?
- Deadwood Reservoir is a lake in Valley County, Idaho. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Deadwood Reservoir?
- Deadwood Reservoir in Valley County, Idaho has a water quality grade of A (Excellent). Water clarity: 17.2 ft visibility. Phosphorus: 14 µg/L. Chlorophyll-a (algae): 1.7 µg/L. Surface area: 3800 acres.
Is Deadwood Reservoir safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Explore Deadwood Reservoir across LakeQuality
4 thermal springs within 11.4 mi, nearest Silver Creek Hot Spring
Species activity outlook by water temperature and season
Where to stay at Idaho's top lakes, each with its grade
Low nutrients, clear water. The letter is not a swimming clearance.
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Other Grade A Lakes in Idaho
Oligotrophic Lakes in Idaho
Where this data comes from
15 measurements from 1 monitoring station, 2012–2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Bureau of Reclamation
1119USBR_WQX15 samples · 2012–2021
Analytical methods
- Depth, Secchi disk depth
- Zebra/Quagga Mussel APHA 10200G Modified
- Phosphorus by Single Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
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.