The pollution of the Tietê River did not start long ago. Even in the 1960s, the river still had fish in the stretch within the capital. However, the environmental degradation of the Tietê River started subtly in the 1920s with the construction of the Guarapiranga Reservoir, by the Canadian firm "São Paulo Tramway, Light and Power Company", for the later generation of electrical energy in the hydroelectric power stations Edgar de Souza and Rasgão, situated in Santana de Parnaíba. This intervention altered the regime of the waters in the capital and was accompanied with some rectification works also by the São Paulo Tramway, Light and Power Company, which left the bed of the river less winding, in the region between Vila Maria and “Freguesia do Ó.”