Scientists and tourists have recently been spotting groups of the rare Yangtze finless porpoise in China's largest freshwater lake, Poyang Lake, raising hopes the endangered mammal is making a comeback.

Guo Ming, a tourist from Shanghai, said he saw six finless porpoises frolicking and leaping out of the water for five minutes at waters in Xingzi County in eastern China's Jiangxi Province.

On March 11, a traffic police officer, Xiong Limin, took photos of nine porpoises at the mouth of the Ganjiang River, the largest tributary flowing into Poyang Lake.

"They swam from east to west, about 50 meters from each other. They disappeared after half an hour," Xiong said.

The amateur sightings coincide with a survey by scientists from the Hydrobiology Institute of the Chinese Academy of Sciences. The researchers caught and released 18 of the mammals between March 2 and 11 in the river's waters in Duchang County, Jiangxi.

Finless porpoises, like white-flag dolphins, are native to China's longest river, the Yangtze, and its numerous lakes. They are afforded the second-level of state protection.

But due to pollution and changes in aquatic ecology, the animals are on the verge of extinction. Only 1,800 porpoises are left in the Yangtze, about half of the population in the early 1990s, said Wang Ding, deputy head of the institute.

Still, the frequent sighting of late indicate the water quality in the lake is improving, said Chen Wenjing, deputy director of the Jiangxi Provincial Fisheries Research Institute.

The provincial government has built 80 water treatment plants to protect the lake, she said.

The Agricultural Ministry set up a monitoring and rescue center in Jiangxi in 2008 and mobilized six provinces and cities to ban the fishing practices that were ensnaring the porpoises.

The ministry is also working to improve the water quality in Poyang Lake, home to one third of the finless porpoise population.