NOTE about Tagus river and estuary

    The Estuary of Tagus is one of the largest in Western Europe. It has an area of 325 km2 and is one of the 10 more important humid areas for aquatic birds in Europe, being endangered by industry and urban pressure. It has an average of 1900 million m3 of water and a saline intrusion occurs until about 20 km from Lisbon. The amplitude of tides in Lisbon varies between 4,2 m and 1,2 m. In terms of mixture of saline water it is partially stratified. The average flow of the river is 400 m3.s-1, varying between 100 and 2000 m3.s-1, according to the months (during flooding it had a recorded  flow of 14 000 m3.s-1). The total area of the watershed is 630 km2, being 31% in Portugal and the remaining 69% in Spain. The river's length is 1070 km.
    The geology of the low
valley is very complex. The last volcanic manifestations occurred 80 million years ago. During the quaternary (within the last 2 millions of years) there were several big oscillations in the sea level (more then 60 m, due to glaciations) and a big variety of flora and fauna developed in the area.