Water temperature helps regulate aquatic ecosystems, and, for many aquatic organisms, life-cycle phases are tied to water temperature. Salmon eggs, for example, generally require a certain number of degree days to hatch. Scientists know that water temperature varies both throughout a day and also within and throughout the seasons. In this study, scientists altered water temperatures to explore how water temperature affects Chinook salmon development. Topics: Water, Wildlife, Adaptation, Dams, Fish Hatchery, Life cycle, Phenology, Salmon.