The freshwater porpoise -- which is known in Chinese as the "river pig" -- mainly lives in China's Yangtze River and two lakes linked to the waterway, and the deaths have raised concern the rare animal is headed for extinction.

Since March, authorities have discovered 10 dead porpoises in Dongting Lake in the central province of Hunan, the official Xinhua news agency said late Wednesday.

Another six porpoise bodies have been found in Poyang Lake in the eastern province of Jiangxi since the beginning of the year, it said.

"The recent deaths brought the mortality rate of the finless porpoise (to) between 5 to 10 percent, which means the species will be functionally extinct in 15 years," Xinhua quoted experts as saying.

Wang Kexiong, a researcher at China's Institute of Hydrobiology, said water pollution, shipping, sand dredging and illegal fishing were all possible causes of the recent deaths.

Many waterways in China have become heavily contaminated with toxic waste from factories and farms -- pollution blamed on more than three decades of rapid economic growth and lax enforcement of environmental protection laws.

Climate change, which has caused water levels to drop and make it more difficult for the porpoises to find food, is another possible factor, the report said.

Tests have shown that some of the porpoises are believed to have died of starvation, it said.

In 2006, China was estimated to have only 1,200 finless porpoises left. That same year, the Baiji -- a freshwater dolphin also native to the Yangtze River -- was declared extinct.

Earlier this year, a survey found just 65 "river pigs" in Dongting Lake and 300 to 400 in Poyang Lake, the report said.

The finless porpoise has been classified as vulnerable by the International Union for Conservation of Nature, a global environment network which groups governments and NGOs.