When living organisms attach to and start living on any object that is submerged in the sea. This is commonly seen as barnacles attached to the hulls of ships or the bodies of whales.

The formation of bacterial film (biofilm) on fragile reverse osmosis membrane surfaces.

Biofouling or biological fouling is the undesirable accumulation of microorganisms, plants, algae, and animals on submerged structures, especially ships' hulls. Biofouling also occurs on the surfaces of all living marine organisms, when it is known as epibiosis. Biofouling is also found in membrane systems, such as membrane bioreactors and reverse osmosis spiral wound membranes.

the gradual accumulation of waterborne organisms (as bacteria and protozoa) on the surfaces of engineering structures in water that contributes to corrosion of the structures and to a decrease in the efficiency of moving parts.

the overgrowth or alage, marine invertebrates, and other organisms on nets, intake pipes,  and structures in the water.  Biofouling can restrict water flow and access to oxygen and food by the growing shellfish.