The more sunlight that hits the water's surface, the warmer the water will get. In addition to shading, the physical dimensions of the waterway will also affect the temperature. Shallow water will fluctuate in temperature faster than deeper water. Running water tends to be cooler than stagnant, still water. In a stream, the shallow riffles or rapids are often cooler than the slow moving, deep pools.
Temperature affects some of the chemical parameters of water.
At lower temperatures, more oxygen can be dissolved in the water because the gas molecules are moving slower and are more compact. At higher temperatures, dissolved oxygen and other gases in water move faster and spread farther apart, including out of the water. Also at higher temperatures, the water molecules may move faster and bump out oxygen. As water temperature rises, it increases the metabolic rates of fish and aquatic insects. Temperature also influences another natural stream process.