Map of All 405 Idaho Dams
Idaho has 405 dams in the National Inventory of Dams — and 105 are classified as high hazard (26% of the state’s total), meaning failure would likely cause loss of life. 4 Idaho dams are both high-hazard and in poor or unsatisfactory condition.
Use the interactive Idaho dams map below to explore every dam in the state, color-coded by hazard level. Click any dam for its condition assessment, last inspection date, and Emergency Action Plan status. Or view the full US Dams interactive map to compare Idaho to every other state.
Hazard
Condition
Purpose
Idaho Dams by the Numbers
- 405 total dams in Idaho
- 105 high hazard — failure would likely cause loss of life
- 141 significant hazard
- 158 low hazard
- 42 in poor or unsatisfactory condition (39 poor, 3 unsatisfactory)
- 4 Idaho dams are both high-hazard AND in poor/unsatisfactory condition
Data source: US Army Corps of Engineers, National Inventory of Dams (NID).
The Tallest Dams in Idaho
The tallest dam in Idaho is Thompson Mtis at 789 feet, completed in 1982. The 10 tallest Idaho dams from the National Inventory of Dams:
| Dam | Height | Year | Primary Purpose | Condition | County |
|---|---|---|---|---|---|
| Thompson Mtis | 789 ft | 1982 | Tailings | Fair | Custer |
| Dworshak Dam | 717 ft | 1973 | Flood Risk Reduction | Not Available | Clearwater |
| Anderson Ranch Dam | 456 ft | 1950 | Flood Risk Reduction | Not Available | Elmore |
| Arrowrock Dam | 350 ft | 1915 | Flood Risk Reduction | Not Available | Boise |
| Lucky Peak Dam | 340 ft | 1955 | Flood Risk Reduction | Not Available | Ada |
| Hells Canyon | 330 ft | 1967 | Hydroelectric | Satisfactory | Adams |
| Palisades Dam | 270 ft | 1957 | Flood Risk Reduction | Not Available | Bonneville |
| Ririe Dam | 253 ft | 1977 | Flood Risk Reduction | Not Available | Bonneville |
| Salmon Falls | 224 ft | 1911 | Other | Fair | Twin Falls |
| Oxbow | 209 ft | 1961 | Hydroelectric | Fair | Adams |
High-Hazard Idaho Dams in Poor Condition
The most concerning dams are those classified as high-hazard that also carry a Poor or Unsatisfactory condition rating — 4 dams in Idaho. Notable examples:
- Magic Dam (128 ft, Blaine County) — Hydroelectric, Unsatisfactory condition
- Fish Creek (92 ft, Blaine County) — Irrigation, Poor condition
- Saint John (43 ft, Oneida County) — Irrigation, Unsatisfactory condition
- Lost Valley (31 ft, Adams County) — Other, Poor condition
Filter the interactive US Dams map by hazard and condition to see all of them on one view.
Dam Safety in Idaho
Dam safety in Idaho is overseen by the state dam safety program, in coordination with federal regulators: the US Army Corps of Engineers, the Bureau of Reclamation (for federal water projects), the Tennessee Valley Authority where applicable, and the Federal Energy Regulatory Commission (FERC) for licensed hydropower dams. Emergency Action Plans are typically required for high-hazard dams under state regulations.
Frequently Asked Questions
How many dams are in Idaho?
Idaho has 405 dams in the National Inventory of Dams tracked by the US Army Corps of Engineers: 105 high hazard, 141 significant hazard, and 158 low hazard.
What is the tallest dam in Idaho?
The tallest dam in Idaho is Thompson Mtis at 789 feet, completed in 1982. It is primarily a tailings structure.
How many Idaho dams are in poor condition?
42 Idaho dams are currently rated as being in Poor or Unsatisfactory condition. Of those, 4 are also classified as high-hazard — meaning failure would likely cause loss of life.
