Filsø in the past
In the Stone Age, Filsø was a large fiord (or bay) on the North Sea, until the formation of points and movement of sand along the coast blocked the sea’s entry more than 4,000 years ago. Filsø became a freshwater lake and the water level rose, reaching seven metres above sea level during some periods. The resulting lake grew to over 3,000 hectares, making it Denmark’s second largest lake at the time, after Arresø.

In 1848, Henne Mill was purchased to drain Filsø. Four years later, the water level of the lake had decreased to just 2.2 metres above sea level, while its size shrank to 750 hectares. In the years 1941-1950, the rest of the lake was reclaimed and cultivated.

The final reclaiming of Filsø resulted in a great loss of natural assets. Meanwhile, more than 1.200 hectares were converted into agricultural land and in 1990 a pig farm with a herd of 560 sows was established at Langodde in the middle of the area.

Nature makes a comeback
A new, shallow lake surrounded by meadows, marshes and reed beds has been re-established in the place of the cultivated fields. The lake has a number of small fox-proof islands and islets where birds can breed. The causeway, which has been raised, runs across the new lake, so it is still possible to walk and cycle across the area. Together with Filsø Heath and Fidde Lake, the natural area measures 2.328 hectares in all.

Some fields have been preserved on both sides of the lake, where geese and red deer can forage for food. New facilities established for visitors include four observation towers, boardwalks, vantage points and car parks. Many kilometres of paths allow visitors to traverse the area while enjoying nature, the new lake and its rich birdlife.

Protecting wildlife
The restoration of Filsø makes the area an extremely important resting place on the “motorway” for migratory birds along the west coast of Jutland. A total of 252 bird species have been sighted at Filsø, of which 235 have been registered since the Foundation’s acquisition. Many birds stay in the lake and surrounding meadows for extended periods, and on some days visitors may see large flocks of Pink-footed Geese, Greylag Geese, Golden Plovers and swans. Distinctive newcomers among the breeding birds at Filsø include White-tailed Eagles, Eurasian Bitterns and Cranes.

Black-tailed Godwits, Ruffs and Black Terns have the opportunity to establish breeding populations and there is hope that Montagu’s Harriers and Short-eared Owls can also breed here in the future.

During the winter season, visitors may see many Peregrine Falcons. In the spring and autumn, large flocks of Starlings form a “black sun” over the water. Impressive flocks of Swallows are often seen in the autumn.

All common waterfowl and birds, such as Ducks, Pink-footed Geese, Grebes, Coots, Grey Herons and Northern Lapwings, now have improved breeding and living conditions.

In the lake, populations of fish such as Roach, Bream, Perch and Pike are being established. A number of habitats for aquatic insects and amphibians have been established in and around the lake. Filsø has already become Denmark’s most species-rich lake for aquatic plants, with 62 different species. The large population of Red Deer enjoy ideal living conditions on the outskirts of the heath.

Welcome to Filsø – dogs are also welcome, but must always be kept on a leash!

A foundation for Denmark’s nature
Aage V. Jensen Naturfond is dedicated to supporting nature conservation and wildlife protection. The Foundation support many nature projects in Denmark, particularly those involving dissemination of know-ledge, and has acquired a number of Denmark’s most important natural areas.