They come in countless forms and live in nearly all kinds of environments. Most are microscopic, growing as single cells, small colonies, or filaments of cells. Phytoplankton grow suspended in open water by taking up nutrients from the water and energy from sunlight. Phytoplankton are classified into groups by the type of pigments they use to perform photosynthesis. Green algae are considered the most closely related to higher plants.
Dinoflagellates are another group of golden-brown algae that also have flagella.
Another flagellated group called the cryptomonads are very small algae and contain pigments that enable them to photosynthesize under very low light conditions, either very deep in the water column or during those times of the year when sunlight isn't very strong. It is important to remember, however, that blue-green algae are very important primary producers in both freshwater and marine systems, despite often being a nuisance. Blue-greens have several characteristics that often enable them to dominate and create nuisance or noxious conditions. Some blue-green species have the ability to adjust their buoyancy. They can float or sink depending on light conditions and nutrient supply.