Summary
In the present paper the authors report preliminary studies carried out during 1975 at freshwater environments at Aripuanã. The research was carried out at Lagoa Cinzenta, a shallow lake situated amidst the tropical rain forest. The influence of heavy inputs of alloctonous material in the composition of the planktonlc community is discussed. The general ecological background of the lake and its importance on the production processes is stressed. Future lines of research are indicated.