The critically endangered Yangtze River dolphin, or baiji, has been sighted in eastern China, Chinese media report.
Scientists had recently declared that the baiji was probably extinct.
An international team of researchers spent six weeks looking for the creature last year without a single sighting.
But earlier this month the baiji was spotted and filmed by a local man, and confirmed by Chinese biologists, says official Xinhua news agency.
"I never saw such a big thing in the water before so I filmed it," Zeng Yujiang from Anhui Province told Xinhua.
"It was about 1,000 metres away and jumped out of the water several times."
Wang Kexiong from the Institute of Hydrobiology at the Chinese Academy of Social Sciences said experts from the institute had confirmed the footage was of a baiji.
Wang Ding, also from the Institute of Hydrobiology and a leading authority on the species, said that the sighting could not be confirmed 100% because of the distance, but that it looked and acted like a baiji.
Wang Ding said a team of scientists would visit the area to see if they could find the creature.
Although the sighting provides a small cause for hope that the creature could survive in the wild, the outlook is not good, says the BBC's East Asia editor Steve Jackson.
In the 1950s there were thousands of Yangtze River dolphins, but numbers have declined drastically due to industrial pollution, heavy river traffic and over-fishing.
A survey by researchers in 1997 found only 13.
If any wild baiji are found scientists will try to capture them and move them to a reserve where they would try to breed them if possible, Wang Ding said.
The last previous sighting of a wild baiji was in 2004, while the last captive baiji, Qi Qi, died in 2002.