This group of water plants grows beneath the surface of the water. The name "oxygenators" is also used for them because they release oxygen into the water during the day as a process of photosynthesis. The primary function of these plants is to remove excess nutrients from the pond, thereby reducing the growth of algae. They also provide spawning areas and protective cover for fish. Certain varieties, such as Hornwort (Ceratophyllum demersum), can either be free floating or anchored in a pot of pea gravel.