Ha Long literally means descending dragon(s) and according to local myth, the story goes as follows:

Long ago when their forefathers were fighting foreign invaders from the north, the gods from heaven sent a family of dragons to help defend their land. This family of dragons descended upon what is now Ha Long bay and began spitting out jewels and jade. Upon hitting the sea, these jewels turned into the various islands and islets dotting the seascape and formed a formidable fortress against the invaders. The locals were able to keep their land safe and formed what is now the country of Vietnam. The Dragon family fell so much in love with this area for its calm water and for the reverence of the people of Vietnam that they decided to remain on earth. Mother dragon lies on what is now Ha Long and where her children lie is Bai Tu Long. The dragon tails formed the area of Bach Long Vi known for the miles of white sandy beaches of Tra Co peninsula