The term UNWANTED PLANT IN A POOL can be summarized as an ALGA, which is a type of aquatic plant. Algae are typically found in freshwater and marine environments, and can range from single-celled organisms to complex multicellular forms. In swimming pools, algae can cause discoloration and cloudiness, and can also clog filters and other equipment. Algae can be difficult to remove, so it is important to take preventative measures to keep them from growing in the first place.