Wild horses and cattle graze on the marshy banks of southern Spain's mighty Guadalquivir River.
From the mouth of this river, Christopher Columbus set off for the New World.
But since then, the river has gotten more salty. As fresh water is extracted for agriculture, drought — made more frequent by climate change — means less rainfall replaces it. Tides send salt water farther upriver.
Inside a cement building straddling part of the river, pumps suck 800 gallons out of the Guadalquivir per second — diverting it to irrigation canals.