The phytoplankton consist of small plants having very limited powers of locomotion or no movement at all. They are mostly subject to distribution by water movements and they photosynthesize, producing the first level in the oceans' food chain.
Certain planktonic algae move by means of flagella, or possess various mechanisms that alter their buoyancy. Most algae are slightly denser than water, and sink into the sediment of the water.
Phytoplankton are largely restricted to lentic ("standing") waters and large rivers with relatively low current velocities.