Situated at the top of the Lesser Antilles chain, only four of the USVI are inhabited: St Thomas (pop. 54,000) is the most developed and can have up to eight cruise ships visiting on some days; neighboring St John (pop. 4,000) is mainly taken up by a national park; St Croix (pop. 55,000), 40 miles (64km) to the southwest, is the largest but poorer and more tranquil than St Thomas. Water Island, off St Thomas, has a few residents and is known as the fourth Virgin Island.