Things did not always go smoothly. In 2008, low temperatures froze the water surface in the reserve and the porpoises were trapped underwater.

Faced with this critical situation, Jiang and his colleagues dug holes in the frozen river surface.

However, the holes froze again and they had to continue digging holes to ensure the animals survived the winter.

Chen Ran, a researcher with the reserve, has witnessed the birth of several finless porpoises. Recently, he has conducted a physical examination of the newborns. The results showed that all the porpoises are in good health.

During the past four years, the city of Tongling has invested about 493 million yuan ($72.8 million) to protect and afforest the shorelines of the Yangtze.

In the city that was previously known for its rich copper resources, a dozen metal producing companies and two sulphuric acid production lines, each with an annual production capacity of 150,000 tonnes, have been closed down.

"Besides environmental restoration, strengthening the genetic study of the animal is urgently required to avoid species deterioration because of inbreeding," he said.

It is also important to restore the food chain by increasing the fish population in the river, he added.