Factors such as temperature, sunlight, oxygen, and nutrients determine which organisms live in which area of the water.Aquatic ecosystems containseveral types of organisms that are grouped by their locationand by their adaptation.Three groups of aquatic organisms include plankton, nekton, and benthos.Plankton are the mass of mostly microscopicorganisms that float or drift freely in the water, and can be microscopic animals called zooplanktonor microscopic plants called phytoplankton.Nekton are all organisms thatswim actively in open water, independent of currents.Benthos are bottom-dwellingorganisms of the sea or ocean and are often attached to hard surfaces.Decomposers are also aquatic organisms.Lakes and PondsLakes, ponds, and wetlands can form naturally where groundwater reaches the Earth’s surface.Humans intentionally create artificial lakes by damming flowing rivers and streams to use them for power, irrigation, water storage, and recreation.Lakes and ponds can be structured into horizontal and vertical zones. The types of organisms present depend on the amount of sunlight available.