The paper describes the light microscope mediated morphometry of widespread centric diatom genera Coscinodiscus and Chaetoceros based on surveys conducted for more than 15 years (2009-2024) in the brackish water realm of the Hooghly River involving sampling sites within the domain of Hooghly-Matla estuarine ecoregion encompassing both mangroves dominated as well as mangrove-devoid coastal areas associated with the Indian Sundarbans. The two genera were selected for the study owing to them being particularly large under their respective taxonomic families. Samples were collected year-round which was segregated into premonsoon, monsoon and post monsoon seasons to differentiate between the physicochemical influence on the distribution of certain species. It revealed the species that were present year-round as well as the seasonal ones. Some of the species observed during the study were not hitherto described from Hooghly estuarine region. The species at least twice recorded within a year were considered for the study to exclude the accidental introductions. A total of 19 species belonging to Coscinodiscus and 23 species under Chaetoceros were documented repetitively throughout the duration of the study. These species are described and illustrated in this article based on observations made under light microscopic objectives.