The results of hydrobiological observations in the "LAGO DE BRASÍLIA", in 1965, presents that lake as a body water in natural state. The biota of Central Brazil waters presents predominancy of Desmidiaceae, autogenetic indigenous plankton, and for example, with species of the genus; Staurastrum, Micrasterias, Euastrum, Cosmarium, Xanthidium, Bambusina, Closterium, Spondilosium, Penium and others, of natural waters. They may be seen, by its latin names, in italic types, in portuguese pages. However, the city of Brasilia has abruptly develloped, in few years arrived to 500.000 inhabitants, in 1968. The influence of the man, and the quantities of his urban nutrients (N, P, K, Ca, Cl, etc. ...) has changed the habitat from a natural lake of desminds (1965) to a lake of Cyanophyceae (1968); with blooms of Aphanizomenon flosaquae, Anacystis cyanea (= Microcystis aeruginosa) Anabaenopsis, Gomphosphaeria, and others blue-algae. the eutrophication index has increased. In accordance with the theory that the Planorbidae mollusks appears from the A-mesosaprobic zone to the B-mesosaprobic one, is supposed a argument because this mollusks followed the migrations of the man; so it is possible to make determinations of the degree of saprobity of waters during the beggining of iniciatory communities of Planorbidae, by hydrobiologic and limnological continuatives studies of the habitat. The authors recommend to take preventive measures as a biologic control over quality of waters of the lake preventing the forthcomming of the molluks of the Schistosomosis. Sanitarity Brasilia sewage is well treated, to protect health and there are no anti-hygienic menaces, but its mineralized nutrients as N, P, K, Ca, Cl, etc. ...provokes great devellopment of blue-algae. The normal eutrophication is excellent producer of nice chlorophyceae plankton and fishes. The authors suggest a new word "HYPEREUTROPHY" for the big and exagerate eutrophication, blowing up tremendous development of phytoplankton, mainly blue-algae. "Hipereutrophy" is without possibility of recovery of normal condictions in waters, without macroscopic life, with turbidity, without self-purification, fomented by enormous source of food supply, artificially produced by man, resulting in continuous blooms of phytoplankton. "Hypereutrophy" is the new name, for a new calamity of waters, condictioned by the impetuosity of the industrialization, and the sudden human populational explosion after the 2nd. world-war. Preventives against the hypereutrophy is proposed in taking indispensable measures by the integrated planning of the rivers and lake basins, providing forestal waters, lakes, and rivers reserves for nature protections. This is possible in a country as the Brazil, because is a nation which is possessor of very big rivers basins, and artificial lakes, yet in indigenous and natural state.