Textural characteristics of the surficial sediments around Perumbalam Island located within the Vembanad Lake, southwest coast of India, were studied on a seasonal basis to understand the geomorphic response of the region. Sediment grain size increased from the northern to southern end of the island, indicating a progressive sorting by tidal currents. In contrast, an increase in the clay and organic carbon content in the sediments of the northern part of region suggests that their distribution is controlled by the productivity of the overlying water column. The evolution of this island is believed to be due to fluvial inputs from Muvattupuzha River. The braid shape of the island is attributed to the high-energy flow along the wedge of the estuary facing the river mouth, which has resulted in a build up of land along the southern boundary. The intense accretion on the southeastern and western sides of the island observed through satellite imagery reveals the fluvial influence on the evolution and morphology of this coastal lagoon.