The temperature of water has extremely important ecological consequences. In general, increasing water temperature results in greater biological activity and more rapid growth. All aquatic organisms have preferred temperature in which they can survive and reproduce optimally. For example, trout typically need cold water which may not be available in shallow waters during the summer.
Temperature is also an important influence on water chemistry.
Rates of chemical reactions also generally increase with increasing temperature. The solubility of important gases, such as oxygen and carbon dioxide increases as temperature decreases. Inversely the solubility of most minerals increases with increasing temperature. Thermal stratification is a common occurance in deep northern temperate lakes such as Onondaga Lake. The vertical temperature profile shown below depicts this layering for a hypothetical summer profile.