The voluminous river Sog – or Sogið – is the largest spring fed river in Iceland. The water is very clear and flows from Thingvallavatn, Iceland's biggest lake. The Sog is 19 km long of which 12 km are passable for salmon but close to the lake are three dams built in the middle of the 20th Century, Iceland's first hydro-power plants. It flows through beautiful and lush landscape, mixed with farmland on the western bank and a birch-forest with numerous holiday-homes on the east bank. The river Sog ends its course when it mixes with the glacial milky waters of the river Hvítá.

The Sog has for many decades been popular with Icelandic anglers. It is famous for its big salmon and also holds large and powerful char. The pristine and clear waters of the Sog, with various pools and long and exciting runs, is ideal for fly-fishing with double handed rods.

The Sog is dived into five beats two of which, Alviðra-beat and Bíldsfell-beat, are now leased by Starir flyfishing club. In the past the beats used to be fished with a mix of fly, bait and spinners but now it's strictly fly only. Although some spots are easily reached with single-handed rods, either from the bank or while wading, double-handed rods give anglers better coverage of many of the runs and pools. It is a wide and powerful river and therefore anglers need to be very careful while wading and life-wests are provided to anglers and strongly recommended.