In algae, the plant body is thallus (a form without root, stem, or leaves).
They are photosynthetic, nucleus-bearing, aquatic organisms.
They are usually marine or freshwater. Some algae can occur in moist habitats like tree trunks, moist soils, and rocks
Algae inhabits mainly at the bottom portion of the water. So, they use light energy to convert CO2 into food.
They increase dissolved O2 in the water body and therefore help fishes in survival.
They also play an important role by minimising the toxic form of nitrogen in the water.
However, excess algae growth or algal bloom is not good for fish, as they deplete the oxygen in water and other vital resources required for the survival of fish.
Examples of algae are - Marimo, green algae, golden algae, etc.