This is a large group of diverse unicellular and multicellular aquatic plants; they grow in both fresh water and seawater and are used commercially as a source of thickeners (agar, agarose, algin, carrageenan) and pigments such as beta carotene. Some countries harvest them as food; Spirulina is produced by Israel and Mexico, and the Japanese consume some species of Chlorella. Some species of algae are important commercial pests because they clog pipes and foul pools and reservoirs.