Freshwaters are inhabited by a remarkable variety of species from most taxonomic groups that have evolved on Earth, but they are also a source of human opportunities, requirements, and conflicts. Strong human impacts have restricted the number and variety of freshwaters and polluted and disturbed many others. This article discusses the range of human impacts and their consequences for species richness and functional diversity of individual lakes and streams. Special emphasis is placed on freshwaters in Europe and North America and their intensely cultivated regions. Biological invasions and climatic changes are not dealt with because of lack of space and paucity of general predictions.