Currently, it is very concerned with the quality of water bodies, especially those of fresh water, considered one of the ecosystems that most suffer from degradation on the planet. Lakes are freshwater ecosystems that have a complex dynamic and that have an important relationship with the fauna present in these environments, being able to act as repositories of biodiversity. The organisms present in these ecosystems can be directly affected by changes in environmental quality. Among the organisms that occur in freshwater environments, macroinvertebrates are among the most abundant. The phylum Mollusca is characterized by bringing together a series of macroinvertebrates that together constitute the second largest diversity in the animal kingdom. They are soft-bodied animals, which may or may not have a shell, inhabiting the most varied aquatic ecosystems. These macroinvertebrates have an important relationship with the biotic and abiotic components of their ecosystems, and their diversity can be used in the environmental assessment of freshwater systems. In these ecosystems there are only two classes of molluscs, Bivalvia and Gastropoda. In Brazil, there are about 115 species of freshwater molluscs belonging to the class Bivalvia and 193 to the class Gastropoda. However, these estimates are imprecise, due to the lack of basic knowledge about their occurrence. Given the anthropic threats to freshwater systems, their biodiversity, the ecological importance of the phylum Mollusca for these ecosystems, as well as the lack of knowledge regarding their occurrence and distribution in Brazil, this research aims to assess the environmental health of lakes. de Santarém through the biological response of freshwater mollusc communities, based on the concept that these animals respond well to environmental changes in their habitats and that such changes can affect their abundance and distribution.