While researching Dongting Lake, the team found only about 150 finless porpoises, about a 40-percent decrease from the figure in 2006 in the same waters, he added.
As the species most strongly associated with the Yangtze, finless porpoises are the barometer of the river's ecological conditions.
The 40-day survey comes after more than 20 of the porpoises were found dead in the Yangtze River and two nearby lakes earlier this year.
The team set off on Nov. 11 from central China's city of Wuhan along the Yangtze River.x It consists of researchers from the Ministry of Agriculture, the Chinese Academy of Sciences and the World Wide Fund for Nature (WWF).
A 2010 WWF report blamed illegal fishing, inadequate water conservancy facilities and pollution in the Yangtze, China's busiest waterway, for the declining number of porpoises.
Snow hits capital of China, flights delayed