The Elwha River runs north out of the heart of the Olympic Mountains in northwestern Washington through more that 70 kilometres of pristine, protected forest into the Strait of Juan de Fuca.

Historically home to all of the migrating salmon species of the region, the once thriving river ecosystem was radically altered with the construction of the Elwha Dam in 1913, followed by the Glines Canyon Dam in 1927.

The dams fuelled an economic boom in Port Angeles, but decimated salmon runs, from nearly 400,000 fish to less than 3,000 a year. This was a devastating blow for the resident Lower Elwha Klallam tribe for whom the salmon are not just a staple food, but the backbone of their culture and economy.

Damming rivers to generate hydro-electricity can produce a clean and renewable source of power, but it does so at a significant environmental cost. Dams disrupt nutrient and soil cycles which not only affect aquatic ecosystems downstream, but have severe impacts on the overall biodiversity of affected rivers.

Protests by the Lower Elwha Klallam tribe were ignored for decades until a growing environmental movement gathered political momentum against the dams. Finally in 2011, the dams were decommissioned and demolition began.

Russell Beard travels to the Olympic National Park in the US, to meet the team of engineers and ecologists working on the largest dam removal project in history.

earthrise can be seen each week at the following times GMT: Monday: 2230; Tuesday: 0930; Wednesday: 0330; Thursday: 1630.

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Source: Al Jazeera