The northwestern Bay of Bengal’s coastal waters are heavily shaped by freshwater discharge from three major rivers: the Ganga, Brahmaputra, and Mahanadi. These inflows influence the region’s bio-optical dynamics, particularly due to the presence of optically active substances like colored dissolved organic matter (CDOM), suspended sediments, and detritus—characteristic of Case-2 waters where such components behave independently from phytoplankton concentrations. Marked seasonal variations in these bio-optical properties are evident, especially during the monsoon when riverine input increases CDOM and sediment levels. Conversely, during non-monsoon periods, phytoplankton absorption becomes more prominent, closely linked with nutrient availability and light conditions, notably affecting the absorption in the blue and red wavelengths. With escalating human activity anticipated in these coastal zones, localized changes in optical properties are expected, underscoring the urgent need for improved, region-specific models to enhance the accuracy of ocean color retrievals from satellite observations.