In Puerto Rico, the main aquatic plant problem areas are along the north side of the island from Rio Grande to Arecibo. Lesser infestations exist in the river systems along the southern part of the island from Naguabo to Ponce and in the southwestern part from Mayaguez through Valle de Lajas to Yauco. The major reservoirs infested are Lago de Cidra, Lago de Loiza, Lago de la Plata, Lago Dos Bocas, Lago Coamo, and Laguna Cartagena. There is relatively little infestation in the streams and lakes of the high mountainous interior. Water hyacinth (Eichhornia crassipes(Mart.) Solms-Lauback) is the major aquatic plant problem, but alligator weed (Alternanthera philoxeroides(Mart.) Griseb.) is likely to become a problem when water hyacinth is brought under control. Chemical and mechanical methods of control have been used with some success. Efforts are underway to introduce biological methods of control that will be more efficient and economical.