Pateira de Fermentelos - a natural lake formed from the confluences of the Cértima and Águeda Rivers. It is the largest natural lake in the Iberian peninsula, and a zone rich in flora and fauna, including species of aquatic birds, such as: the Little Bittern, Purple Heron Kingfisher, Western Marsh Harrier, Black Kite and various types of duck.[13] In addition, local fish, such as Largemouth bass, Esox, Carp, Mullet, and Perch, and the commercial popularity of Crayfish and Rays, support the freshwater fishing industry of the region. - Taken from Wikipedia