Þingvallavatn is a lake in south-western part of Iceland. The surface of 84 km ² is the largest natural lake in Iceland. Its greatest depth is 114 m. On the north shore of the lake at Thingvellir (which is named after the lake) is Althing, the national parliament, founded in 930th.
The lake is part of the National Park Thingvellir. Volcanic islands in the lake is clearly visible.Cracks generated by the movement of tectonic plates earth, are Almannagjá canyon..The waters from Lake Þingvallavatn are flowing to Sog river.