Something is lurking in the deep in China's famous Yangtze River - and social media discussion is rife over what it might be.
On Friday, footage appeared on China's popular Sina Weibo microblog of what appeared to be a long, black creature, manoeuvring through the waters, and it has dominated online discussion ever since.
Footage has quickly racked up millions of views, and theories are rife.
Specialists have weighed in - but some think there may be a simple, and less murky, explanation.
Excitement over footage
A video filmed off the coast of the city of Yichang in western Hubei province, close to the Three Gorges Dam, captured the unusual scene.
The video has racked up more than six million views and hundreds of thousands of likes after being shared by the popular Pear Video, and shows what looks like a giant eel or snake slithering along the surface of the water.
Locals are filmed watching the creature from the shore - and social media users have similarly been captivated over theories about what the creature might be.
Many have posted using the hashtag #ThreeGorgesMonsterPhotos, and specialists have begun to weigh in with their thoughts.
In an interview with Pear Video, Professor Wang Chunfang from the Huazhong Agricultural University dismissed the idea of it being a new species, saying it was likely a simple "water snake".
Some users said that "external factors such as pollution" could have a role to play in a sea snake growing to an extraordinary size. But not everyone was convinced.
Separate footage has led some users to question whether the unidentified object is actually a living creature at all.
Popular news website The Paper shared separate footage of something long and black moving in the water that appeared to be less animated.
It asked if the whole thing was simply "a rumour" - and interviewed a biologist, Ding Li, who said that the object was neither a fish nor a snake, but simply "a floating object".
A picture has since gone viral showing a long piece of black cloth washed up on some rocks, fuelling discussion this might have been the mysterious object.
Both have led to jokes about whether the local government was trying to attract tourism to the area, given the millions of dollars involved in building and maintaining the Three Gorges Dam.
Others have made jokes about the quality of the footage, despite the rapid development in China of high quality smartphones.
Some joked that the user obviously didn't have a Huawei phone. Another said: "Monsters always appear only when there are few pixels."
So what does live in the Yangtze?
The Yangtze River is the longest river in Asia, and at 3,900 miles in length (6,300km), is the third longest in the world.
But pollution has severely affected the river in recent years, meaning that its ecosystem has become narrower, rather than wider.
The largest creature thought to exist in the waters at present is the Chinese giant salamander, which can reach some 1.8m in length.
This species is critically endangered, largely as a result of pollution.
China's other 'Nessies'
China is no stranger to conspiracy theories about mythical creatures lurking in the deep.
Since 1987, questions have been asked about whether a "Lake Monster" exists in the Kanas Lake in north-western Xinjiang, following numerous reports of sightings.
However, specialists believe that this is a giant taimen, a species of salmon that can grow to 180cm long, the official China Daily said.
More recently, in August 2017, footage went viral showing an unusual water creature seemingly raising its head in the waters of Luoping County in Southwest Yunnan province.
Officials, however, dismissed the "monster" as either an alligator, or a piece of floating rubbish.