Las Marismas, Spanish for "The Marshes", is a large area of marshland in Andalusia in Spain.

Formation of Las Marismas

Twenty-five centuries ago, a large bay existed at the mouth of the Guadalquivir River in southwest Spain.

Twelve centuries later the bay had been transformed into an enormous salt lake.

Since then, the lake has become a trackless marshland which.

This transformation was caused by silt transported by the Guadalquivir and the power of strong sea currents

Sand swept along the coast from the west gradually formed a sandbank across the bay, impounding a shallow sea. The river's cargo of silt and mud, brought down from the Sierra Morena and other inland mountains, drove out the salt water and created shallow lagoons in its place.

This barrier is known as Arenas Gordas or "fat sands". It contains a long series of beaches and sand dunes.

Life on Las Marismas

Las Marismas is boarded by biologically diverse habitats, such as dune heath, savanna and the remains of cork-oak forests. These provide sanctuary for many birds, including the cinereous (black) vulture and the Spanish imperial eagle, and several mammalian species, such as the Iberian (Spanish) lynx.

The Seasons


Las Marismas undergoes radical seasonal changes. Heavy rains sweeping across southern Spain in late autumn inundate the western slopes of the Sierra Nevada and the plain of Andalusia.

The silt-laden water drains into the Guadalquivir, which, in turn, floods Las Marismas, often to a depth of 60cm (2ft).

The wetland environment provides a welcome stopping-off point for many waterfowl migrating south for the winter, as well as a winter home for many ducks and geese returning from their summer breeding grounds in northern Europe and Scandinavia.

For a few weeks, Las Marismas is turned into a noisy, bustling crossroads for a million avian migrants.

In spring, when the mountain snows melt, fresh water descends to the marshes. At the same time, the rise in temperature stimulates plants to grow.

Thick stands of grasses, reeds and rushes spring up on elevated islands, or vetas. They conceal an enormous number of bird nests.

In early May, swarms of midges, mosquitoes and dragonflies emerge from their pupal stages, luring birds to the area.

Many bird species gather together to feed and mate. These include herons, flamingoes, black-winged stilts, turnstones and plovers, ruddy shelducks, red-knobbed, or crested, coots and the marbled teals.

Red kites and cinereous vultures fly over Las Marismas searching of lizards and small mammals. Egrets and spoonbills form nesting colonies in ancient cork oak.

Meanwhile, the Iberian lynx makes a lair in dense thickets of bramble and jaguarzo.

Within a few weeks, the Guadalquivir ceases to top up the marshes. The sun's heat intensifies and evaporates the water.

In dwindling water channels, rushes and grasses grow in ever thickening clusters while green algae accumulate in huge clumps.

Large mammals appear in increasing numbers.

By June, herds of red deer and fallow deer splash through the water to reach succulent grasses. Wild boar shuffle across drier ground.

By early August, the grounds of Las Marismas have been transformed to hard, cracked mud.