Lake Masvatn has an area of 3,96 km². Its greatest depth is 17 m and it is situated 265 m above sea level on road no. 1 a short distance west of lake Myvatn.

A few brooks spill into it and its discharge is Maslaekur, which tributes the Reykjadalsa river. The catch consists of brown trout and lake char of equal size, 1-3 pounders.

The distance from the capital is about 469 km  by the Whale Bay tunnel and 80 from Akureyri.