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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.

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We assessed the distribution of alien fishes in one of the most ecologically and economically important aquatic ecosystems in Iran, the Karun River Basin. Fish samples were collected from 35 sites in the Karun River Basin during the low-flow period from November to December 2018. We documented the occurrence of 37 species of fishes from nine orders and 14 families. Amongst these, 10 species were alien (986 individuals; 15.7%). The relative abundance of native, endemic, and alien species estimated as 54.8%, 29.5% and 15.7%, respectively. Total length of alien species ranged from 0.4 to 25.5 cm and their total weight from 0.17 to 350 g. The ten alien species belonged to seven families including, Cyprinidae, Cichlidae, Xenocyprididae, Gobiidae, Poeciliidae, Gobionidae, and Salmonidae. Carassius gibelio, Oreochromis aureus, and Coptodon zillii were found to be the most abundant alien species in the downstream region. We applied redundancy analysis (RDA) as a direct stressor method to identify the extent of changes in alien fish assemblages with environmental parameters. The first two axes (RDA1 and RDA2) accounted for 36.24% and 25.33% of the variation of five alien species, respectively. Altitude, depth, electrical conductivity, water temperature, turbidity, dissolved oxygen, and river width were the most significant parameters affecting the distribution of alien species. Our results propose that management practices are needed in the downstream sections of the Basin to recover native and endemic species. Monitoring of presence and extent of alien species is a key to measuring the success of these efforts.