During 1982 and 1983, more than 100 algal samples were collected from several sites of infestation. All samples were examined under the microscope with the exception of Chara species. The identification work was limited to the genera. The predominant genera identified were Hydrodictyon, Spirogyra, Rhizoclonium and Oedogonium. Other less abundant genera were Anabaena, Aphanizomenon, Bacillaria, Chara, Chlorosarcina, Cladophora, Closterium, Cosmarium, Diatoma, Eremosphaera, Fragilaria, Gyrosigma, Hormidium, Nannochloris, Navicula, Oscillatoria, Pithophora, Phacus, Protococcus, Pyrobotrys, Roya, Scenedesmus, Spirulina, Synedra, Symploca and Ulothrix. The relative abundance of these genera of algae on different rice farms in Puerto Rico is also reported.