Hong Kong is in the sub-tropical region, and its marine environment supports species of both tropical and temperate climate. Local waters contain a wide diversity of fishes, crustaceans, molluscs and other marine life, of which at least 150 species are of significant fishery importance.

          Local waters are under the strong influence of Pearl River, the largest river in southern China. Set on the eastern bank of the river's estuary, Hong Kong receives freshwater discharged from the river, especially in its western waters. The eastern waters, on the other hand, are little influenced by the Pearl River outflow and have a predominantly oceanic characteristic. This special hydrographic condition helps to contribute to the high diversity of marine life found in Hong Kong.

          Despite being close to the northern limit for hard corals, Hong Kong supports some 50 true coral species. This diversity of corals is considered quite rich by international standard. The green sea turtle is seen in local waters and nests in Hong Kong on a remote sandy beach of Lamma Island. A variety of marine fishes also breed in Hong Kong waters. Typical of eastern waters is the red sea bream, one of the several sea bream varieties whose fry are abundant along the shores of Mirs Bay in early spring.

          Despite the small size of Hong Kong waters, two marine mammal species can be found here all year-round. The better-known one is the Indo-Pacific hump-backed dolphin, also locally known as Chinese White Dolphin. A recently completed study indicates that one dolphin population appears to be centred in the Pearl River Estuary, including Hong Kong's western waters around Lantau Island. It is estimated that the Pearl River dolphin population contains more than 500 individuals.

          A study has been commissioned to collect information on the biology of the finless porpoise, the other resident marine mammal species in Hong Kong. Unlike the Chinese White Dolphin, this species is frequently seen in eastern and southern waters, but is rarely found in the western waters preferred by the Chinese White Dolphin. It appears that there are seasonal shifts in finless porpoise numbers, probably resulting from an offshore movement of porpoise south of the Hong Kong boundary.

          There has been concern over the degradation of the marine environment by pollution, coastal development works, over-fishing and destructive fishing practices. To counteract the disturbance to inshore marine resources, artificial reefs are being deployed to enhance fisheries resources and the biodiversity of the marine environment. The Marine Parks Programme continues to serve as an important tool to protect and conserve sites of special ecological and conservation values.