Kárahnjúkar Hydropower Plant (Icelandic Kárahnjúkavirkjun) is a hydroelectric power plant in eastern Iceland designed to produce 4,600 gigawatt-hours (17,000 TJ) annually for Alcoa's Fjardaál aluminum smelter 75 kilometres (47 mi) to the east in Reyðarfjörður. With the installed capacity of 690 megawatts (930,000 hp), the plant is the largest hydroelectric power plant in Iceland. The project, named after nearby Mount Kárahnjúkur, involves damming the Jökulsá á Dal river and the Jökulsá í Fljótsdal river with five dams, creating three reservoirs. Water from the reservoirs is then diverted through 73 kilometres (45 mi) of underground water tunnels and down a 420-metre (1,380 ft) vertical penstock towards a single underground power station.