Can bacteria reveal hidden pollution? New river study says yes

The Guadalquivir is the most important river in Andalusia. Stretching 657 kilometers (408 miles), it forms the backbone of Andalusia, from its source in the Sierra de Cazorla mountains to its mouth in Sanlúcar de Barrameda. These facts, along with its name of Arabic origin (Wadi al-Kabir) and its strategic role in the economy, agriculture and tourism, are widely known. Few studies, however, have comprehensively assessed the quality of the "Great River" along its entire course.

Raccontata daphys.org