1. Introduction
Nowadays, only the main course of the Guadalquivir
River functions as an estuary and its water quality is currently affected by two major classes of pollutants: organochlorine pesticides from the surrounding agricultural area, and heavy metals, mainly
from Aznalc´ollar mine (Baluja et al., 1985; Cabrera et al., 1987). Despite this environmental damage, the
Guadalquivir Estuary (the largest estuary in the Gulf of Cadiz) continues to play an important role as a nursery
area for many marine fish species (Fern´andez-Delgado et al., 2000).