Coastal lakes are shallow lakes that have variable characteristics through fluctuations and marine winds. In this study, benthic diatom composition in the coastal lake of Iztuzu, Dalyan of Mugla was investigated from the material collected in 2011 and 2015. Little research has been done on coastal lakes and lagoon diatom flora in Turkey; this study contributes a total of 49 taxa identified to species level and 9 of the taxa for the first time recorded for diatom flora of Turkey. The most abundant taxa were; Cocconeis placentuta Ehrenberg, Diploneis bombus (Ehrenberg) Ehrenberg, Mastogloia sp. and Chamaepinnularia alexandrowiczii Witkowski, Lange-Bertalot and Metzeltin. The results reveal a habitat-specific flora for Iztuzu Lake and give an aspect of understanding the marine-brackish distribution of diatoms in coastal lakes and lagoons. The results extend the knowledge of marine and brackish diatoms in Turkey and could provide data for similar lagoon and lakes which are under protection.