Lake Miklavatn has an area of 6,6 km². Its greatest depth is 23 m and it is situated at sea level. A few brooks and rivers empty into it and its discharge spills into the sea through a narrow gravel reef.
The lake abounds in sea char and sea trout and some salmon runs through it for the river Fljotaa. Lake char and brown trout are also caught in the lake, as well as a few species of sea fishes (cod, plaice, herring).
The distance from the capital is about 390 km, 36 km from Hofsos and 24 km from Siglufjordur.