Lake Arreso

Arreso covers about forty square kilometres, which makes it the largest lake in Denmark, and it sits in a shallow basin in north Zealand with an average depth of only about three metres, so it is more a wide sheet of water than a deep one, fringed with reed beds, wet meadow and alder carr. In the eighteenth century a canal was cut from its western end to Roskilde Fjord to drop the water level and drive mills at Frederiksvaerk, which is how that industrial town came into being. The shore is a mixture of nature reserve, farmland and small settlements, with birdwatching along the reed edges for grebes, geese, marsh harriers and sea eagles, and a long-distance path and cycle route running round most of the perimeter.

What you actually see

• Denmark's largest lake - forty square kilometres and only metres deep.
• Reed beds and wet meadow - the fringe where the birds are.
• The Arreso canal - the eighteenth-century cut to Roskilde Fjord.
• A circular path and cycle route - most of the way round the shore.

When to go

April to October for the walking and the birds; autumn and winter bring geese and sea eagles. Half a day for a section of the shore, a full day to cycle round. Dawn is the hour for birds.

Honest expectations

The lake is shallow and can look flat and featureless in dull weather. There is no continuous public access along the whole shore; some stretches are private. Swimming is limited and algae blooms occur in warm summers. Facilities are scattered.

Nearby

Gribskov lies east; Frederiksvaerk and Roskilde Fjord are west.