The presence of algae is a necessary condition for the normal life of water bodies. Fish and other aquatic animals feed on algae. Algae absorb carbon dioxide from water and, like all green plants, release oxygen, which not only dissolves in water (and is breathed by living organisms that live in water), but is also released into the atmosphere.
Man actively uses algae. In many countries, algae (kelp (seaweed), ulva (sea salad), porphyry, etc.) are used to prepare a variety of dishes. They are very useful because they contain a lot of carbohydrates, vitamins, and are rich in iodine. They produce iodine, potassium salts, cellulose, alcohol, acetic acid and other products.
Algae is used as fertilizer and fed to livestock. Some types of red algae produce a gelatinous substance called agar-agar, which is necessary in the confectionery, bakery, paper and textile industries. Microorganisms are grown on agar-agar for use in laboratory research.
Chlamydomonas, chlorella and other unicellular green algae are used in biological wastewater treatment.