Benthic zone
The benthic zone is the ecological region at the lowest level of a body of water
Body of water
A body of water or waterbody is any significant accumulation of water, usually covering the Earth or another planet. The term body of water most often refers to large accumulations of water, such as oceans, seas, and lakes, but it may also include smaller pools of water such as ponds, puddles or...

 such as an ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

 or a lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos
Benthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone. This community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.Many organisms...

. They generally live in close relationship with the substrate bottom; many such organisms are permanently attached to the bottom. The superficial layer of the soil lining the given body of water, the benthic boundary layer
Benthic boundary layer
The benthic boundary layer is the layer of water directly above the sediment at the bottom of a river, lake or sea. It is generated by the friction of the water moving over the surface of the substrate...

, is an integral part of the benthic zone, as it influences greatly the biological activity which takes place there.