Conservation experts say that pollution and development are killing off the Chinese white dolphin, known for its white-and-pink spotting, which has lived in the Hong Kong's waters since the 17th century.
"They are diminishing their use [of Hong Kong waters], they are not reproducing and they are dying," Dr Samuel Hung Ka-yiu, chairman of the Dolphin Conservation Society, told the South China Morning Post on Sunday.
"It is hard to say if they will leave Hong Kong permanently … but [the trend] will become worse and worse," he said.
According to the World Wildlife Federation, Chinese white dolphins, also known as Indo-Pacific humpback dolphins, are considered "near threatened" by the International Union for Conservation of Nature.
The largest population of the species lives in the seas around Hong Kong and Macau, also known as the Pearl River Delta.
Hung said that the numbers of pink dolphins living around Hong Kong would shrink "significantly" in a report due out next month. They counted 158 in 2003 and just 78 in 2011.