A preliminary systematic and ecological study of seventy four species of phytoplankton in Nenguange Bay was carried out during the year 1974-1975. Weekly changes in species diversity (numbers of species plus a relative measure of abundance), were recorded along with temperature and salinity. It was noted that with the beginning of the rainy season the largest phytoplankton bloom occurred especially in the diatom flora. During this time, salinity was at a minimum and temperature at a maximum.