Wikipedia
Nisser is a lake in Norway. It is the 13th-largest lake in the nation by area with a surface area of 76.30 km², the 10th largest by volume at 7.19 km³, and the 13th deepest at 234 m. It is located in Nissedal and Kviteseid municipality in Telemark county, and is Telemark’s largest lake. Part of the Arendal watershed, water enters from the discharge of Vråvatn, and its outlet is the Nisserelva river.
In 1914, a canal was constructed between Nisser (which is 246 m above sea level) and Vråvatn (which is 248 m above sea level). This makes it possible to travel the 50 km long stretch from Tveitsund to Vråliosen by boat.
The Norse form of the name was Nizir - probably from an older form *Niðsær. The meaning of the name is 'the lake (sær) of the river Nið (now Nidelva (Aust-Agder))'.