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There is much evidence that climate is rapidly changing at a global scale, especially regarding mean annual temperatures, precipitations and evaporation. The consequences of this rapid environmental change on freshwater biota are still not clear, but undoubtedly they could be severe. Among the main effects of climate change, we can individuate the enhancement of water temperatures, particularly important for poikilothermic organisms, with the consequent diminution of dissolved oxygen, and the reduction of available habitats for most stenothermal organisms. Another consequence of climate change is the alteration of hydrologic cycles, with increasing intensity and frequency of extreme events such as droughts, especially in Southern Europe. This scenario could severely affect freshwater biota, especially in mid-latitude regions, such as the Italian peninsula: shifts in phenology, life cycles and distribution ranges are likely to be expected for many organisms, with the extinction of many sensitive species. In particular, species adapted to perennial and cold waters are likely to suffer reductions in their distribution range and also local extinctions, while more tolerant organisms may enlarge their distribution ranges. Global climate change may also promote and enhance invasions of alien species. In this work, concepts and hypotheses about the presumable impacts of climate change upon freshwater biota are reported, with examples and predictions related to the Italian situation.

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