The Alte Waterfall (better known as Queda do Vigário ) is the terminal part of a sequence of waterfalls formed in limestone tuffs found on the Alte river in Alte , in the municipality of Loulé , in the Algarve , Portugal . Limestone tuff is a type of rock formed in waters of karst origin that, after losing carbon dioxide, become supersaturated in calcium carbonate that accumulates at the bottom of water courses, in waterfalls, lakes or any other aquatic environment. It is popularly called a dam.