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National Marine Fisheries Service, Alaska Regional Office

Prince William Sound

Habitat Conservation Division - Hydropower Program

Traditional Hydropower Projects

Bradley Lake Dam, Homer, AK Bradley Lake dam outside of Homer, AK. Photo: NOAA Fisheries

Traditional hydropower projects in Alaska are typically lake-taps, run-of-river projects, or less commonly, dammed rivers. New technology is being developed to harness the power of free-flowing rivers with in-stream hydrokinetic turbines, and tidal and wave power hydrokinetic projects are in experimental stages of development within the state's marine waters.

Lake-tap projects in Alaska use a natural alpine lake as a reservoir and divert water downhill through an intake and penstock to turbines in a power plant that turn to produce electricity. Often a tunnel is bored through the mountain directly into the bottom of the lake. Sometimes a siphon is used to divert water from the lake into the penstock. Outflow water is returned via a tailrace to the lake's outlet stream, to a different stream or directly to saltwater. Lake-tap projects change the hydrologic flow regime of the lake - often obvious 'bathtub rings' are created on the lakeshore as lake levels fluctuate. They have the potential to dewater the bypass reach of the stream, change lake levels, create fish passage barriers, and alter habitat by other means. These projects often have small dams on the natural lake outlet that increase the storage capacity of the lakes.

Run-of-river projects typically divert water from a river or lake, using the hydraulic head available with steep terrain to turn a turbine near sea level to produce electricity, and then return the flow downstream to the same river or stream. They do not alter the natural hydrograph by storing water, but rather use water as it is naturally available on a seasonal basis. Run-of-river projects often dewater streams for a short reach resulting in fish passage barriers, potential impingement and entrainment of fish, and alteration of habitat.

Dammed rivers work similarly to lake taps, but a the river is dammed to create a reservoir that stores water during high flow events. Dams on rivers alter stream flow and habitat. The environmental effects of dammed rivers include: changes to stream flow; pulsing flows and associated habitat effects; the reservoir traps debris and sediment necessary for downstream channel maintenance; dams create barriers to upstream and downstream fish passage and other aquatic life; fish habitat is lost and there can be an associated decrease in fish survival; water quality is affected (typically temperature and dissolved oxygen resulting from the storage of water in a reservoir).

NMFS's Habitat Conservation Division reviews existing and proposed hydropower projects and advises the FERC on ways to minimize adverse effects to anadromous fish.

Alaska Hydropower Projects


Project Information


Existing Projects


Proposed Projects

  • Little Port Walter (non FERC)
  • Thayer Creek (non FERC)