Trong Mai Islet (Fighting Cock Rocks) is situated on the southwest side of HaLong Bay, 5 km from the tourist wharf near Dinh Huong Islet. In a somewhat large expanse of open sea, the island seems to grow up from the bottom of the deep emerald waters. At sunset, the over 10 m high islet turns bright red.and because the tiny rock “legs” support the heavy rocks above, it appears that one strong wave could throw the large stone blocks into the sea. However, hundreds of millions of years have passed, and the Trong Mai is still there. An image of this island is the logo of  HaLong Bay and Vietnam Tourism.

Ha Long Bay also supports a number of fish-farms which supply seafood to the rest of Vietnam and other countries.   Marine biologists and their students study the ecology of the area and help develop markets for the farmed sea grass, seaweed, algae, fish and shrimp. Farther offshore, where populations of shrimp, fish, squid, abalone, and other sealife exist,   thousands of tons of food are caught annually.