Jianggudiru Glacier on Geladaindong mountain, in China's western province of Qinghai.
One of the largest glaciers at the source of the Yangtze River, the glacier is fast retreating because of climate change, said state media.
Chinese Academy of Sciences researcher Pu Jianchen told Xinhua news agency that the glacier has shrunk 34m over the past six years.
He said it began to shrink slowly in the 1970s, then expanded between 1989 and 1994 before retreating more quickly from 1995, Xinhua reported late on Tuesday.
Mr Yang Xin, president of the Green River Environmental Protection Association, said the retreating of the glacier is "direct evidence of global climate change".
Mr Pu said the Yangtze would get more water in the short term as the glacier and others melt, but eventually, no more water would flow from them. China, the world's biggest greenhouse gas emitter, has promised to bring emissions to a peak by "around 2030" as part of a global pact to combat global warming that was signed in Paris last year.