Heat is considered as a water pollutant because it decreases the capacity of water to dissolve oxygen, and it increases the rate of metabolism fish. Valuable species of game fish cannot survive in water with very low levels of dissolved oxygen.
Proteins which form channels may be utilized to enable the transport of water and other hydrophilic molecules; these channels are often gated to regulate transport rate. In facilitated transport, hydrophilic molecules bind to a "carrier" protein; this is a form of passive transport
