From the Greek neustos- floating.

Neuston - a set of organisms living directly within the surface film of water. A distinction is made between epineuston - organisms moving along the surface film from above and hyponeuston - organisms living below the surface film.

A set of microorganisms (mainly various algae and small invertebrates) living near the surface film of water at the boundary between the aquatic and air environments (in the so-called "neustal"). There are epineuston, which includes organisms living on the water surface, and hyponeuston, which includes organisms attached to the surface film from below or living in water no deeper than a few millimeters from the surface.

Neuston films are formed, as a rule, in standing water bodies (lakes, swamps, puddles, ditches, etc.), but can also appear in large water bodies on a relatively small area of calm water (without waves). Neuston inhabitants often multiply in such masses that they become visible to the naked eye, and the number of organisms per 1 mm² of surface area can reach several tens of thousands.

The main part of freshwater neuston consists of algae of various departments: golden algae (Chromulina), euglena algae (Euglena, Trachelomonas), green algae (Chlamydomonas), yellow-green algae (Botrydiopsis) and others. Neuston, represented by a relatively small number of species, includes some protozoa, small pulmonary mollusks, water bugs, spinner beetles, mosquito larvae and a number of other small organisms. Marine hyponeuston y sometimes also include permanent or temporary inhabitants of the uppermost layer of water (0-5 cm), such as fish fry, larvae of some bottom animals.

Many neustonic microorganisms have special adaptations (various growths, "sails") or characteristic morphological features (presence of gas vacuoles in the cells, abundance of oil in the form of cellular inclusions, covering the cell with mucus, etc.) for retention in the surface layer of water.

Neuston is called the incubator of the sea. Neuston is the first to die when oil pollution occu.