Lake Hlidarvatn is 4,7 km long and up to 1,7 km wide. It has an area of about 4,4 km² and is situated 78 m above sea level. Its discharge is the river Hraunholtsa, which enters lake Oddastadavatn.
The fishing permits are limited to the western part of the lake. The catch consists of lake char and brown trout and late in the summer there is a vague hope for a salmon to bite. The lake char usually weighs less than a pound but the brown trout 5-6 pounds. In 1964 an unsuccessful attempt was made to operate a floating hotel on the lake.
The distance from the capital is 108 km by the Whale Bay tunnel and 50 km from Borgarnes.