Lake Hnjuksvatn has an area of 0,72 km² and is situated 595 m above sea level. Very little visible water can be seen in its catchments area but its discharge, river Hnjuksa, tributes to the glacial river Jokulsa a Bru. It is accessible by 4wd vehicles and the catch consists of lake char. The lake is netted.
The distance from the capital is about 624 km by the Whale Bay tunnel and 70 km from Egilsstadir.