Glaciers act as reservoirs of water that persist through summer. Continual melt from glaciers contributes water to the ecosystem throughout dry months, creating perennial stream habitat and a water source for plants and animals. The cold runoff from glaciers also affects downstream water temperatures. Many aquatic species in mountainous environments require cold water temperatures to survive. Some aquatic insects--fundamental components of the food web--are especially sensitive to stream temperature and cannot survive without the cooling effects of glacial meltwater. Such changes in stream habitat may also adversely impact native trout and other keystone salmon species.