Other people claimed to have seen a similar animal earlier in the month.
There have been loads of "monster sightings" at the lake since the start of the last century.
The same sense of mystery surrounds Scotland's Loch Ness, where many people have claimed to have seen a weird creature.
It's become so well known that it's got a nickname - Nessie.
A BBC team recently carried out a search of the lake and claimed there was no evidence that Nessie existed.
It seems the scientists are out to prove China's monster doesn't exist either.
They say the lake is so cold that such a big creature would never survive in it.