Morphological changes on Sagar Island are occurring at an alarming rate due to both natural and anthropogenic activities. The eastern part of the island is rapidly eroding due to destabilization and growth of tidal flats in the Muriganga estuary and the gradual shifting of water current towards the island. Over the last four years (1996–1999), the rate of coastal erosion has been much higher (11.35 km2) than accretion (2.65 km2), compared with the conditions prior to 1996. Coastal places like Dublat, Basantpur, Gobindapur, Collectorganj, and Sumatinagar have become the critical zones of erosion. The shorelines along the eastern and south‐western sides are receding. The extent of coverage of the paddy field, sandy beaches, and land vegetation has decreased from 1996 to 1999 by 15.7, 1.1, and 3.5 km2, respectively. An integrated database of the island was generated using spatial and non‐spatial data collected through field survey, satellite images of IRS‐1C LISS III, and topomaps. Spatial data include coastal geomorphological landforms, land‐use and land cover, shoreline change, sandy beaches, coastal erosion sites, agricultural fields, aquaculture sites, and coastal riparian vegetations. Non‐spatial data include the demography and evolution of the island. The main critical environmental issues of the island are: (1) degradation of mangrove forests and coastal erosion; (2) overpopulation and over‐exploitation of living resources; and (3) destruction of seawalls. Further degradation may lead to extinction of a variety of species and scarcity of marine food unless properly managed and regulated.