Hafravatn is a lake within the boundaries of Mosfellsbær. The lake is 1 km² in size, with a maximum depth of 28m and an average depth of about 8m . Although it is little known as a fishing lake, one can still get good fishing there. The lake is best known during winter and is popular for ice fishing. There are a lot of small char in the lake and some brown trout that are a little bigger. Salmon also enters the lake through river Korpa, but not many salmon are caught in the lake.