Hornindalsvatnet is Norway's and Europe's deepest lake, officially measured to a depth of 514 metres (1,686 ft). Its surface is 53 metres (174 ft) above sea level, which means that its bottom is 461 metres (1,512 ft) below sea level.
The village of Grodås lies at the eastern end of the lake in Volda Municipality in Møre og Romsdal county and the village of Mogrenda is located on the western end of the lake in Stad Municipality in Vestland county. The European route E39 highway runs near the lake. The village of Heggjabygda and Heggjabygda Church lie on the northern shore of the lake.
Its volume is estimated at 12 cubic kilometres (2.9 cu mi), its area is 50 square kilometres (19 sq mi) and ranks 19th in area among Norway's lakes. The main outflow is the river Eidselva, which flows into the Eidsfjorden, an arm off the main Nordfjorden.
The deepest point of the lake was explored using a ROV in 2006. A small white fish was discovered on the lake bottom – probably a new species of Arctic charr (Salvelinus alpinus). It was previously also located in Lake Tinn, Norway's third deepest lake.The lake is also the site of the Hornindalsvatnet Marathon, held annually in July.