The response of freshwater organism groups to selected stressors has been described in numerous studies. Although the type and severity of human-generated pressures affecting the integrity of lakes, rivers, wetlands and groundwaters varies across the world, the major drivers can be summarised as multiple use (such as fisheries, navigation, water extraction, nutrient enrichment and organic pollution, acidification and habitat degradation).
Among these factors, habitat degradation at catchment scale that includes the alteration of hydrological regimes is the single most important cause of freshwater species extinction, contributing to the endangerment of 85% of the threatened species in the USA. However, there are only a very limited number of studies comparing the response of different organism groups to multiple-stress situations. Climate Change (see WP5) is adding supplementary stressor types (temperature increase, hydrological changes) and interacts in complex ways with other stressors.