Ha Long Bay is in northeastern Vietnam, from E106°56´ to E107°37´ and from N20°43´ to N21°09´. The bay stretches from Yên Hưng district, past Hạ Long city, Cẩm Phả town to Vân Đồn district, bordered on the south and southeast by the Gulf of Tonkin, on the north by China and on the west and southwest by Cát Bà island. The bay has a 120 kilometre long coastline and is approximately 1,553 square kilometres in size with 1969 islets. The area designated by UNESCO as the World Natural Heritage Site includes 434 km² with 775 islets, of which the core zone is delimited by 69 points: Đầu Gỗ island on the west, Ba Hầm lake on the south and Cống Tây island on the east. The protected area is from the Cái Dăm petrol store to Quang Hanh commune, Cẩm Phả town and the surrounding giants zone.
Climate
The bay is a sea islands in tropical wet with 2 seasons: hot and moist summer, dry and cold winter. Average temperature is from 15°C- 25°C. Annual rainfall is between 2000mm and 2200mm. Ha Long Bay has the typical diurnal tide system (tide amplitude ranges from 3.5-4m). The salinity is from 31 to 34.5MT in dry season and lower in rainy season.