SummaryThe four periphytic communities established in Plover Cove Reservoir (the epiphyton, epihthon, epipelon and epipsammon) were investigated between November, 1970 and December, 1971. A rich flora of diatoms was found to dominate all four peri‐phytic communities, and, for this reason, assessment of diatom numbers was used to monitor each community during this survey.The standing crop of each community, measured by cell counts and by chlorophyll a determinations, showed distinct seasonal patterns. Except for the epipsammon, each community displayed a maximum growth in winter, a moderate spring and autumn growth period and a low summer growth. The episammic flora stood apart from the other attached floras in that it exhibited a prolonged maximum growth period in summer.Relatively small numbers of species were found to form the main bulk of all four communities (the so‐called ‘constant forms’) and these belonged predominantly to the pennate genera Achnanthes, Fragilaria, Nitzschia and