Some 2,000 years ago, , the shallow bay that is now known as  the Doñana region began to become a great delta thanks to marine sand deposits and contributions of river sediments. The great Guadalquivir River was divided into many arms that lined those emerging tidal marshes.

In the past century due to agricultural and commercial interests of the region and the city of Seville, great works of transformation of the Guadalquivir River course took place and resulted in the shortening of the length of the main branch and the gradual loss of functionality of secondary branches.

The so called Brazo del Este (Eastern Branch) is nothing but the bed of the original largest east branch of the main channel, which surrounded the so called Isla Menor (Lesser Island). Today it zigzags among farm fields where rice dominate and is still recognizable by the natural vegetation that grows in it.

This mosaic of agricultural land and natural vegetation at Brazo del Este attracts for most of the year a large variety of waders, raptors and passerines. Rice harvest works in autumn put the number of waterfowl attracted by the easily available food up very quickly.

The main dirt road that cuts the Brazo and the old Carretera del Práctico (Coast Pilot Road), which runs along the Guadalquivir River, are the main access points, but to these must be added an intricate network of secondary roads and channels that make navigation difficult in the area, hence the usefulness of a local guide.

Featured species: Booted eagle as wintering, squacco heron, black stork, glossy ibis, marbled teal, purple swamphen, penduline tit, bluethroat, spanish sparrow.