This stream is included in the Doñana Natural Park because it is an ecological corridor between Doñana National Park and the Sierra Morena.
In 1997, the Arroyo de Pilas was included in Doñana Natural Park because of its ecological and environmental values. This 12-kilometre corridor, described as a seasonal stream in the Mediterranean region, boasts up to 50 varieties of plants and many more animals, of which 42 are bird species. This stream, a tributary of the River Guadiamar, rises in Manzanilla (Huelva) at an altitude of 170 metres.
The middle course of the Arroyo de Pilas marks the boundary between Hinojos and Pilas, separating the provinces of Huelva and Seville. The stream is known by different names in the province of Seville. In the upper course, it is called Arroyo de Pilas; in the middle section, Arroyo de Gato; and, in the lower, Arroyo de la Cigüeña. This last section is channelled and flows into the overflow channel of the River Guadiamar, in the area known as El Rincón del Puerto in the Doñana marshes.
The Arroyo de Pilas has one of the best-preserved riparian forests in Doñana when it passes through Pilas. This strip of riparian vegetation is in contact with woodland pastures, such as the Peru (SCI) and Torrecuadros (SAC) dehesas. The Iberian Lynx populates the latter area and uses the Arroyo de Pilas as an expansion zone towards other territories. There are many riparian vegetative species, among them, black poplars, white poplars, ashes and willows, as well as bush vegetation. In flood-prone areas, there are reeds, bulrushes and rushes.