Algae is a microscopic, unicellular protist that forms the base of the food chain. Algae can be found on the bottom of ponds or lakes before it floats to the top. Algae has a musky smell and can be bright or dark green. Algae is a small but beneficial plant found in ponds and lakes. The three most common types of algae are Chara algae, filamentous algae, and pond scum. Algae can be harmful if it accumulates on the surface of a pond or lake. Algae is planktonic and turns the water into a pea soup color. Algae can reduce the levels of oxygen in water, which can kill fish. Multiple treatments are necessary to prevent this from happening.