Algae is a common term for the pond scum you often see floating on top of your water body. Algae, however, are more than just these floating mats. Algae are the simplest form of plants that can range from individual cells on the microscopic level, to large plant like structures called macro algae. Algae does not have a true root system, which allows it to grow anywhere in the water body. Algae are generally classified into 3 different groups: Filamentous algae, Planktonic algae, and Chara.