Kárahnjúkar Hydropower Plant ( ), officially called Fljótsdalur Power Station ( ) is a hydroelectric power plant in Fljótsdalshérað municipality in eastern Iceland, designed to produce annually for Alcoa's Fjarðaál aluminum smelter to the east in Reyðarfjörður. With the installed capacity of , the plant is the largest power plant in Iceland. The project, named after the nearby Kárahnjúkar mountains, involves damming the rivers Jökulsá á Dal and Jökulsá í Fljótsdal with five dams, creating three reservoirs. Water from the reservoirs is diverted through of underground water tunnels and down a vertical penstock towards a single underground power station. The smelter became fully operational in 2008 and the hydropower project was completed in 2009. The Kárahnjúkar Dam ( ) is the centrepiece of the five dams and the largest of its type in Europe, standing tall with a length of and comprising of material. The project has been heavily criticised for its environmental impact and its use of foreign workers. Description The hydroelectricity project harnesses the rivers Jökulsá á Dal and Jökulsá í Fljótsdal by creating three reservoirs with five concrete-face rock-filled embankment dams; three on the Jökulsá á Dal and two on the Jökulsá í Fljótsdal. After being used in the Fljótsdalur Power Station, all water used in electricity production is discharged into the river Jökulsá í Fljótsdal. Three dams on the Jökulsá á Dal; the Kárahnjúkar Dam (), the Desjará Dam () and the Sauðárdalur Dam () create the Hálslón Reservoir. At tall and long, the Kárahnjúkar Dam is the largest dam in the project and the largest of its type in Europe as well. The tall and long Desjará Dam and the tall and long Sauðárdalur Dam are saddle or auxiliary dams that maintain the desired height of the Hálslón Reservoir. Water from the long, capacity Hálslón Reservoir (about the size of Manhattan island in New York) is diverted down a long, diameter headrace tunnel towards the Fljótsdalur Power Station. On the river Jökulsá í Fljótsdal, the tall and long Kelduá Dam forms the capacity Kelduárlón Reservoir. Downstream from the Kelduá Dam is the tall, long Ufsarstífla dam which forms the Ufsarlón, a much smaller reservoir. Water from the Ufsarlón Reservoir is diverted down a long, diameter headrace tunnel where it joins the Hálslón Reservoir headrace tunnel. Before each of the headrace tunnels from the Hálslón Reservoir or Ufsarlón Reservoir reach the underground power station, they both