Human activities and the unplanned occupation of land in aquatic basins can drive cultural eutrophication, which leads to the degradation of water quality, an increase in the concentrations of nutrients, and the depletion of biodiversity. This chapter will describe the basic concepts of trophic status, ecological changes, and alterations to the composition of freshwater biodiversity, as well as current threats and global perspectives of these issues. Additionally, selected case studies from Brazilian freshwater using benthic macroinvertebrates in urban reservoirs and cyanobacteria in semiarid lentic ecosystems are discussed.