Approximately two
millennia ago the
wetlands comprised a large
lagoon and
estuary, known as in Latin, leading to the
Guadalquivir River mouth with some sand bars to the South. Over time the
lake silted up, gradually transforming into
marshland. This silt has formed into a barrier of dunes extending approximately along the coast, known as
Arenas Gordas (English: "the fat sands"). In the early 21st century, the Guadalquivir wetland region's main economic activity is
agriculture, specialising in the cultivation of
rice. An area of about 400 km2 is devoted to
rice farming. It has an annual output of about 310,000 metric tonnes, equating to approximately 40% of Spain's rice production. ==Protected area==