| Ah Pah Dam | |
| Country: | United States |
| Location: | Humboldt County, Northern California |
| Status: | Unbuilt |
| Owner: | U.S. Bureau of Reclamation |
| Dam Type: | Concrete thick arch |
| Dam Height: | 813feet |
| Dam Length: | 3500feet |
| Dam Crosses: | Klamath River |
| Res Capacity Total: | 15000000acre.ft |
| Res Catchment: | 14700sqmi |
| Plant Capacity: | 900–1,700 MW |
Ah Pah Dam was a proposed dam on the Klamath River in the U.S. state of California proposed by the United States Bureau of Reclamation as part of its United Western Investigation study in 1951. It was to have been 813feet high and was to be located 12miles upstream of the river's mouth. It would have been taller than any existing dam in the United States and it would stand almost as tall as the Transamerica Pyramid building in San Francisco, but would have been much more massive. It would have flooded 40miles of the Trinity River, including the Yurok, Karuk and Hupa Indian Reservations, the lower Salmon River, and 70miles of the Klamath River, creating a reservoir with a volume of 15000000acre.ft – three fifths the size of Lake Mead, and over three times the size of the current largest reservoir in California, Shasta Lake. The water would flow by gravity through a tunnel 60miles long to the Sacramento River just above Redding and onward to Southern California, in an extreme diversion plan known as the Klamath Diversion. The tunnel would have been located near the southernmost extent of the reservoir. It was named in the language of the Yurok people.