Toxic strains of the finely filamentous, velvety, dark-olive green to black algal organism, Microcolus Lyngbyaceus, (formerly Lyngbya majuscula Gomont, or "lyngbya") have been recognized as etiologic agent of "stinging seaweed" dermatitis (one of several forms of "swimmer's itch") in Hawaii since the late 1950s as reviewed. Lymphadenopathy, pustular folliculitus, and local infections have been reported in some persons.