Plant pathogens have characteristics that make them desirable candidates as biological control agents for aquatic weeds. They are: (1) numerous and diverse; (2) often host specific; (3) easily disseminated and self-maintaining; (4) capable of limiting populations without eliminating the species; and (5) non-pathogenic to animals. Recent investigations have revealed several pathogens with biocontrol potential. The algal viruses and the water hyacinth (Eichhornia crassipes (Mart.) Solms-Laub.) pathogens, Acremonium zonatum (Sawada) Gams, Bipolaris stenospila (Drechs.) Shoemaker, Cercospora rodmanii Conway, Rhizoctonia spp and Uredo eichhorniae Fragoso and Ciferri have been researched the most extensively and appear to hold promise as biocontrol agents.