Arresø

The Arresø is a lake in the Capital Region on Sjælland, north of Ølsted and east of Frederiksværk in Denmark.

With 39.87 km ² of lake area is Denmark's largest lake. It is connected with the Roskildefjord by a canal, which was begun about 1717 by Danish and Swedish soldiers prisoners of war. The lake borders the Hillerød municipality, Gribskov municipality, the municipality and the Halsnæs.

The average depth of the lake is 3.1 m, the greatest depth 5.6 m. The lake contains about 122.75 million cubic meters of water. The most important of the tributaries of the lake is the POLEA. East of Frederiksværk is the Arrenæs peninsula that juts into the lake from the west.

The lake was a fjord, which was connected to the Kattegat about 4000 years ago. By raising the country in the northwest of the fjord created during the last ice age, the lake today.