Not only can dolphins be pink, but they come in two different varieties: the Amazon river dolphin, and the Chinese white dolphin. The latter, also known as Sousa chinensis, has seen its population shrink in recent years, and now conservationists have warned that the species is at risk of disappearing completely from Hong Kong waters, as reported by the Guardian.

Despite the name, Chinese white dolphins have pink skin due to a prominent, near-surface network of blood vessels, somewhat overdeveloped in order for them to regulate their body temperature. They draw huge crowds of tourists to the northern shoreline of Lantau Island each and every day.

Although always popular, the species rose to particular prominence when it was declared the official mascot of the 1997 handover ceremony, wherein the United Kingdom returned the Hong Kong archipelago over to China. However, campaigners say that there are only 60 pink dolphins left – a huge drop from 158 in 2003. This is equivalent to a 62 percent loss over the last 12 years.

The causes of this dramatic decline in pink dolphin numbers are entirely human. As an island city state, Hong Kong has an incredibly busy waterway transportation system, with bustling ferries and ports shuttling the autonomous territory’s 7.2 million residents back and forth across one of the world’s most densely populated metropolises.

Image credit: Charting the disappearance of Hong Kong’s pink dolphins. Hong Kong Dolphin Conservation Society

As the population and tourist influx both increase year on year, larger transportation hubs, including airport infrastructure, is built out into the sea. Currently, Hong Kong is seeking to expand its international airport by constructing a major new bridge; in addition, a third runway at the busy Chek Lap Kok airport is likely to be approved of.

This expansion of infrastructure inevitably destroys the habitat of the pink dolphin, while simultaneously causing highly disruptive noise and water pollution. The population of Hong Kong-based pink dolphins are either dying out, or migrating to less chaotic Chinese waters.

In particular, the third runway would take up a large chunk of their remaining habitat, and may cause the disappearance of the pink dolphins in this region altogether. “We think that if that project goes ahead, then it will probably drive the dolphin away from Hong Kong waters,” said Samuel Hung, chairman of the Hong Kong Dolphin Conservation Society, in a statement. He has been going out to sea at least twice a week to monitor dolphin activity for almost 20 years.

“In some ways it seems like we are pushing them closer and closer to the edge of the cliff and if we're making that final push, they will be gone forever. I think now is the time to get our act together.”

The large, 50-kilometer (30-mile) bridge connecting Lantau Island to the nearby enclave of Macau has only worsened the situation; the associated land reclamation that began in 2012 has encroached on huge swaths of the pink dolphin’s habitat.

The government has issued a statement on the issue, stating “a new marine park of approximately 24 square kilometers (9.3 square miles) in the waters north of the third-runway project has been proposed.”

However, campaigners were quick to pour cold water over this announcement, saying that by the time the park is completed by 2023, the local pink dolphin population may have already died out.

“We don't even know whether the dolphin can hang on and survive and wait,” Hung added.