However, not all blue-green algae are blue-green. Black, brown, yellow, red, grass green and other colors also occur.
Some of these organisms are also able to fix free nitrogen in a fashion similar to bacteria. Reproduction in blue-green algae is by cellular fission as in bacteria. Reproduction of this major group is asexual.
Blue-green algae occur in numerous and varied habitats. They most frequently occur in masses, either floating or attached to some object in water. Some species are very common in or on soil, others are often found growing on the sides of damp rocks and on the bark of trees. They tend to be particularly abundant on wet cliffs and ledges. Many are mainly inhabitants of fresh waters.