Salsette(साष्टी) (Portuguese:Salsete, Marathi:Sashti(साष्टी)) is an island in Maharashtra state on India’s west coast. The metropolis of Mumbai (formerly Bombay) and the city of Thane lie on this island.
The present island was formerly made up of several smaller islands, which were joined together during the 19th and early 20th centuries to form a single island. It is bounded on the north by Vasai Creek, on the northeast by the Ulhas River, on the east by Thane Creek and Bombay Harbour, and on the south and west by the Arabian Sea. The city of Mumbai lies on a peninsula on the southern end of the island, and Mumbai’s suburbs cover much of the remainder of the island. The island contains Borivali National Park, also known as Sanjay Gandhi National Park. The city of Thane lies at the island’s north-eastern corner, on Thane Creek. The coordinates are approximately 20° N and 72° E. Politically, most of the island falls into the municipality of Mumbai. The municipality is divided into two separate districts, Mumbai City and Mumbai Suburbs. The northern portion of the island lies within Thane District, which extends across Vasai and Thane creeks onto the mainland.
Parts of the island are hilly, although many of the hills were cut down and used to enlarge the island by filling in the shallows and to link the islands to one another. The highest point on the island is around 450 metres in the Borivali National Park, in the northern reaches of the island. This National Park is the world’s biggest within city limits.
The island is located at the confluence of a number of fault lines. This makes the area earthquake prone, up to a magnitude of 6. The island is mostly composed of black basalt rock. Since it is along the sea coast, it also has a sandy belt on its western coast. The southern region of Old Bombay is mostly at sea level. However, the parts which were erstwhile shallows are below sea level. Many parts of the city are hilly.
There are three major lakes on the island Powai Lake, Tulsi Lake and Vihar Lake. The latter two lakes supply part of the city’s water requirements. Numerous other smaller ponds and lakes are also present in the Thane region. On the shores of the Powai lake lies the celebrated Indian Institute of Technology Bombay.
Three small rivers, the Mithi (Mahim), Oshiwara and Dahisar, originate within the National Park, and empty into the Arabian Sea. The Mithi River originates from the Powai Lake. Vasai and Thane creeks are estuarine distributaries of the Ulhas River.
A number of saline or brackish creeks extend inland from the coastline. The Mahim creek separates the city from the suburbs in the west, and the Sion Creek in the east (Sion creek no longer exists). Further north on the western coast, the Oshiwara river empties into the Malad (or Marvé) Creek and the Dahisar River into the Gorai Creek. The eastern waterfront too, has many small creeks.
The small southern part of the eastern waterfront of the island forms the Bombay harbour. North of this region lie vast amounts of protected wetlands, home to migratory birds. The northern, north western part of the island and parts of Mahim River also have government protected marshlands. These swampy regions form massive and dense mangrove forests.
The western coast of Mumbai has numerous beaches. The best known is the Girgaum-Chowpatty Beach. Other well known beaches are Dadar Beach, Juhu Beach, Mahim Beach, Gorai Beach and Worli Beach; of which Juhu and Gorai Beaches lies on west cost of Sashti (साष्टी) island.