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Special nature

Zwanenwater near Callantsoog

Behind the dunes south of Callantsoog lies Zwanenwater, an almost intact landscape with two large natural dune lakes, broad reed and marsh zones, wet valleys, heath and open sand. Spoonbills, cormorants and marsh birds use the lakes and banks for breeding and feeding. In May and June, thousands of orchids colour parts of the valleys pink and purple. Grass-of-Parnassus and heath follow later, while large flocks of ducks rest on the water in autumn and winter.

Special natureNature & landscapeDune lakes and wet dune valleysNature area
A large dune lake with reed-fringed banks and dunes in Zwanenwater nature reserve near Callantsoog
One of the large dune lakes of Zwanenwater. Open water, reed marshes, wet valleys and dry dunes lie close together here.Photo: MatsAlkmaar, via Wikimedia Commons, CC BY-SA 4.0Changes: No changes.

Why go here?

Zwanenwater shows how a complete freshwater landscape can lie behind a narrow coastal strip. Two large lakes are surrounded by reeds, great-fen-sedge marshes, orchid-rich valleys, heath and dry dunes. Walking paths, viewpoints and bird hides reveal open water, breeding colonies and flower-rich hollows without entering the most vulnerable areas. An admission ticket is required, but no guide is needed.

What do you see?

The First and Second Water lie among broad reed beds, great fen-sedge, willow scrub and wet grasslands. Higher ground supports dune heath, grassland, open sand and small woodland patches. Waterbirds, cormorants and sometimes spoonbills can be watched from the bird hides. Orchids and singing bluethroats stand out in spring, followed later by Grass-of-Parnassus and heath. Routes may be wet or sandy in places and do not pass through every vulnerable zone.

What can you see when?

Choose a month to see which animals, plants or fungi are most likely then.

Broad-leaved and southern marsh orchids

Plant

In May and June, thousands of pink, purple and reddish-violet orchids may colour the mown wet dune valleys. The exact flowering period depends on water level, temperature and management.

Grass-of-Parnassus

Plant

The white finely veined flowers appear later than most orchids. Grass-of-Parnassus grows mainly in damp nutrient-poor places influenced by clean groundwater.

Cross-leaved heath and crowberry

Plant

In summer and late summer, parts of the old acidic dunes turn purple. Cross-leaved heath favours damp ground, while crowberry also covers drier decalcified dunes.

Eurasian spoonbill

Bird

Spoonbills may breed or rest on islands and quiet banks. In shallow water, they sweep their flat bills from side to side in search of small fish and aquatic animals.

Great cormorant

Bird

Cormorants occur on and around the lakes throughout most of the year. Nests, commuting birds and individuals drying their spread wings are especially conspicuous in spring.

Bluethroat

Bird

From April, males sing from reeds, low willows and marsh scrub. The bird is often heard first and may briefly appear on top of a stem or shrub.

Eurasian bittern

Bird

The bittern almost always remains hidden in extensive reed beds. Its deep booming display call may carry across the water in spring. Seeing one in flight remains a fortunate encounter.

Bearded reedling

Bird

Bearded reedlings move low and nimbly through reed beds. Their pinging calls often reveal a small group before the birds become visible among the stems.

Eurasian wigeon and northern shoveler

Bird

From late summer and especially in autumn and winter, ducks gather on the large lakes. Wigeons often rest in flocks, while shovelers filter food from the water with their broad bills.

Goosander

Bird

Goosanders may appear on the open lakes, particularly during cold winter periods. These long slender ducks actively dive for fish.

Natterjack toad

Amphibian

On mild evenings, a prolonged rolling call may sound from shallow pools in the wet dune valleys. The toads themselves usually remain hidden among low vegetation and sand.

Sand lizard

Reptile

Sand lizards may bask on sunny sheltered dune slopes and beside open sand. Move quietly and watch the edges between low vegetation and bare ground.

Why it matters

Zwanenwater is among the best-preserved mainland dune landscapes in the Netherlands. Because it was never used for drinking-water extraction, natural water levels and the transitions between lake, marsh, wet valley, heath and dry dunes remained relatively intact. This connected landscape supports rare plants, breeding and migrating birds, amphibians, reptiles and insects. Its extensive nutrient-poor wet dune vegetation is particularly exceptional.

The deeper story

Zwanenwater lies behind the foredunes south of Callantsoog. From the coast, it is difficult to imagine that two large freshwater lakes lie among the dunes. The First Water and Second Water form the centre of a landscape containing reed marshes, wet dune valleys, heath, grasslands, open sand and small woodland patches. The North Sea is close, but rainwater and groundwater shape the area.

The present landscape developed through centuries of storm floods, coastal erosion and recovery. By the late Middle Ages, the old dune ridge had been severely broken and the Zijpe tidal inlet penetrated far inland. Construction of the Zijper sea dyke followed the severe storm flood of 1553. New dune ridges subsequently formed on its seaward side. Water became trapped between them and initially created one elongated dune lake.

Windblown sand later narrowed the lake in several places, producing the First and Second Water. Broad reed beds, great-fen-sedge marshes, willow scrub and wet grasslands developed around the shallow lakes. Farther from the water lie wet valleys, acidic heath, dry dune grasslands and open sand. Very different habitats therefore occur within short distances.

An important difference from many other mainland dunes is that Zwanenwater was never used for drinking-water extraction. Artificial abstraction and infiltration profoundly altered the hydrology elsewhere. Here, natural fluctuations in rainwater and groundwater remained far better preserved. This allowed wet valleys and nutrient-poor vegetation to survive over large areas.

The two lakes are among the largest natural dune lakes in western Europe. Reed, tall sedges, great fen-sedge and willows line their banks. Great fen-sedge forms dense stands of tall, sharp-edged leaves. Bluethroats, sedge warblers, bearded reedlings, water rails and bitterns live among the reeds and marsh vegetation. Marsh harriers hunt low above the vegetation. Cormorants breed in colonies, while spoonbills sweep shallow water for small fish and aquatic animals.

Outside the breeding season, the lakes become resting places for ducks. Wigeons, shovelers, gadwalls and tufted ducks gather on the open water. Goosanders may appear during colder periods. Other waterbirds use the area as a stopover during migration along the nearby North Sea coast.

The wet dune valleys are at least as remarkable as the lakes. In May and June, broad-leaved and southern marsh orchids may flower by the thousand. Grass-of-Parnassus and other plants associated with clean, nutrient-poor groundwater follow later. Cross-leaved heath, crowberry and peat mosses grow in more acidic, strongly decalcified sections. A difference in height of only a few centimetres may determine how long a place remains wet and which plants can grow there.

Without management, open valleys and heath would gradually become overgrown by tall grasses, shrubs and trees. Parts of the area are therefore mown, grazed or stripped of their top layer. Cut material is removed to keep the soil nutrient-poor, and sand is allowed to move again in selected places. Management aims to preserve variation rather than simply opening everything.

Open sand and temporary pools are also valuable. Sand lizards bask along sunny transitions between bare soil and low vegetation. Natterjack toads use shallow pools in the valleys and produce their rolling calls on mild spring evenings. Dragonflies, butterflies, bees and hoverflies benefit from the combination of water, shelter and flower-rich dune grasslands.

Walking routes deliberately remain away from the most vulnerable plant sites and breeding colonies. Bird hides and viewpoints provide views across the lakes without repeatedly disturbing resting birds. An admission ticket is required. No guide is needed, but sturdy footwear is sensible because sections of the route may be wet, loose or uneven.

The landscape changes strongly with the seasons. Pale reeds, open water and bare dunes dominate early spring. May and June bring orchids and intense birdsong. Grass-of-Parnassus flowers later in summer, and parts of the heath turn purple in August. The lakes become increasingly important for ducks and other winter visitors during autumn and winter.

The complete structure becomes visible from the higher dunes. The North Sea lies to the west and the polder to the east. Between them, open sand, heath, wet valleys, reed marshes and dark water surfaces follow one another. These short distances allow spoonbills, orchids, natterjack toads and sand lizards to live within the same reserve.

Zwanenwater is therefore more than two beautiful lakes. Reed fringes tell the story of natural infilling, orchids reveal clean groundwater, heath marks old decalcified dunes and open sand represents continuing renewal. Together they form a rare freshwater landscape behind the coastal dunes.

Further reading