This runoff also moves faster into the stream than would natural runoff because it travels through straight concrete or plastic storm drain pipes. This increased volume and velocity of runoff scours the stream channel and widens it. During dry weather between storms, the channels have a very shallow flow. These wide, shallow streams heat up much more quickly than do more natural narrow, deep ones. Additionally, black surfaces, like many streets and parking lots, absorb heat, and rainwater moving over these surfaces during storm events becomes warmer.
Some industries use water as a coolant during processing.
This water is sometimes discharged to a stream or lake. When this water is discharged to a creek, it is much warmer than the water in the creek, and the temperature of the creek becomes higher. This phenomenon is called thermal pollution. This can cause the period of ice cover on the water to be shortened, and can increase the metabolic rate of plants and animals, producing an increase in oxygen demand. This is another form of thermal pollution.