Zayandehrud Dam Lake located in Isfahan province is the largest lake in central Iran. In this study, the plankton communities including phytoplankton and zooplankton were studied as bioindicator organisms for assessment of water quality in the Zayandehrud Dam Lake. The water and phytoplankton organisms were collected from four stations at different seasons during 2014 by using a Nansen bottle sampler. The zooplankton samples were collected with a plankton net (mesh size = 50 µm). The phytoplankton community was composed of Bacillariophyceae, Cyanophyceae, Euglenophyceae, Dinophyceae and Chrysophyceae. The zooplankton community viz; Cladocera, Rotifera and Copepoda were found to have a density range of 13–155, 21–141 and 11–93 (ind. m−3), respectively. In general, phytoplankton and zooplankton communities, especially the presence of genera such as Cyclotella, Dynobrion, Bosmina and Daphnia (as indices of oligotrophic lakes) and also absence of Microsystis, Brachionus and Lecane are seen as important indices of eutrophic lakes. It could be concluded that the Zayandehrud Dam Lake can be classified as a healthy water body.