Arresø is the largest lake, by area, in Denmark. It covers 40,72 km2 and is situated on the island of Zealand 43 kilometers northwest of Copenhagen as the crow flies.
Arresø is located in the northern parts of Zealand in the region of Hovedstaden just north of Ølsted and east of Frederiksværk. It is a part of the three municipalities Gribskov, Halsnæs, and Hillerød. The lake empties into Roskilde Fjord through the Arresø Canal in Frederiksværk.
