All aquatic organisms have a fairly well-defined temperature tolerance range and this determines their distribution. Temperature affects the saturation concentration of dissolved oxygen (as seen in Table 2). An increase in water temperature will reduce the oxygen solubility as well as increase the metabolic activity of aquatic organisms. The combination of these two effects means that oxygen demand by organisms increases just when oxygen supply is being reduced.
Coarse fish such as perch, roach and chub can tolerate water temperatures up to 30°C and dissolved oxygen levels as low as 3 g m−3. However, game fish such as salmon or trout die if the oxygen concentration drops below 5 g m−3 or if the water temperature moves outside the 5–20°C range.