Flatningen is a lake in Vågå Municipality in Innlandet county, Norway. It is located on the far eastern edge of the Jotunheimen mountain range. The 2.35-square-kilometre (0.91 sq mi) lake lies about 8 kilometres (5.0 mi) south of the village of Vågåmo and about 9 kilometres (5.6 mi) west of the village of Lalm. The lake Lemonsjøen lies about 4 kilometres (2.5 mi) to the southwest of this lake.