Dissolved Oxygen Content in Water vs. Temperature

Fish movement is keyed to two main factors, temperature and the oxygen content of the water. Fish will seek out areas of a water-body that satisfy both of these needs. While the coldest water can hold the most oxygen (see Table 1) the cycles of a lake can dramatically alter the amount of oxygen present in a particular temperature zone, more on this in a future post.

Cold, clear streams and rivers hold the most oxygen while warm, still water will hold the least. The various cold-water, cool-water and warm-water species will gravitate to areas where both preferred temperature and sufficient oxygen is present. High fertility lakes can have seriously depleted oxygen levels at greater depths. Algae blooms and decaying matter will also lower oxygen levels.

In winter, ice and snow cover can also cause oxygen depletion as plants can no longer produce oxygen due to lack of light.

More on how all this affects fish movement in the following post.

References:
1) http://water.epa.gov/type/rsl/monitoring/vms52.cfm