Sog is the largest freshwater river in Iceland in terms of water volume. Average flow is 110 m³/s. It runs from Lake Þingvallavatn for 21.9km to its confluence with the river Hvítá, forming the river Ölfusá which then runs for another 25 km into the Atlantic Ocean.
There are three hydroelectric power stations in the river: Ljósafossstöð (15 MW), Írafossstöð(48 MW) and Steingrímsstöð(27 MW).
Sog River runs through two lakes, Lake Úlfljótsvatn and Lake Álftavatn.
The river has a healthy stock of arctic char and Atlantic salmon. The size of the char can be anywhere from 0.5 pounds up the 5.0 pounds with an average size of 1.0 pound. The most common weight for salmon is 5.0 to 10.0 pounds with a few fish caught each year from 20.0 to 30.0 pounds. There are also sea-run brown trout in the Sog River.