Mumbai Harbour (Marathi: मुंबई बंदर Mumba'ī bandar), or Front Bay (sometimes referred as Mumbai Harbour), is a natural deep-water harbor in the southern portion of the Ulhas River estuary. The narrower, northern part of the estuary is called Thane Creek. The harbor opens to the Arabian Sea to the south. The historical island of Elephanta is one of the six islands that lie in the harbor.