Water depth :
As depth below the surface increases, the amount of sunlight available to aquatic plants decreases. Some plant species have anatomical, cellular or biochemical adaptations that allow them to carry out photosynthesis successfully in deep or murky water despite the decreased availability of sunlight.
Sunlight :
Most plants and many bacteria get their food by photosynthesis. ... Aquatic plants get water and carbon dioxide from their aquatic environment and, like the land plants, light energy from the sun. Even though the plant is underwater, it still gets its energy from the sun because sunlight can pass through water.
