Hálslón Reservoir reshapes Iceland’s east with water, concrete and conservation

On the highlands of eastern Iceland, a vast artificial lake known as Hálslón Reservoir marks a dramatic intersection of engineering and nature. Created to power the Kárahnjúkar Hydropower Plant, the reservoir stands as one of the country’s major infrastructure projects and has shaped both the local landscape and Iceland’s approach to conservation.

Shaping valleys with three dams

Hálslón Reservoir was formed by damming the flow of the Jökulsá á Dal River, along with waters from Kringilsá and Sauðá. At the heart of this operation is Kárahnjúkastífla, a colossal dam measuring 193 metres in height and 730 metres in length. Built using 8.5 million cubic metres of rock and concrete, it ranks as the largest concrete-faced, rock-filled embankment dam in Europe. Its imposing height, however, meant that water behind it would naturally spread sideways into neighbouring valleys, so two additional embankments, Desjarárstífla to the east (60 metres tall, 1,000 metres long) and Sauðárdalsstífla to the southwest (25 metres tall, 1,100 metres long), were constructed as auxiliary dams. Together, these three dams brought a new body of water into existence on Iceland’s highland plateau.

Engineering on the project began in 2003. By September 2006, the main Kárahnjúkastífla Dam was sealed, and the slow filling of Hálslón began. The reservoir reached its full extent at the end of 2007, with a surface elevation rising to 625 metres above sea level. Spanning 25 kilometres in length and up to 2 kilometres in width, the water level can vary as much as 75 metres between maximum and minimum, though normal yearly fluctuations are usually less extreme.

Water to electricity, and a changing landscape

All this water has a purpose: at peak, up to 2.1 cubic kilometres is harnessed for hydropower, flowing at an average rate of 107 cubic metres per second through the Kárahnjúkar plant’s turbines. After generating electricity, water is channelled back into the Jökulsá í Fljótsdal river and, eventually, into Lagarfljót, one of Iceland’s significant watercourses.

The creation of Hálslón brought profound change to its environment. The region’s waterfalls, Kringilsárfoss and Sauðárfoss among them, vanished beneath the rising water. To protect the natural surroundings from further loss, the Icelandic parliament granted the surrounding area park status in 2005, before the reservoir even finished filling. This single act placed a staggering one-tenth of Iceland’s total surface under legal protection.

TopicsHálslónhydropowerIcelandic highlandsJökulsá á DalKárahnjúkastífla