Langavatnet is a lake in the municipality of Odda in Hordaland county, Norway. The 6.19-square-kilometre (2.39 sq mi) lake lies about 10 kilometres (6.2 mi) straight east of the town of Odda. The lake has a dam at the north end to regulate the water level for the purposes of hydroelectric power generation. The water of the lake previously flowed north to create the large Ringedalsfossen waterfall which now only flows when the lake gets too full.