Lake Baikal is an ancient lake situated in Siberia. It is the largest freshwater lake in the world when measured by volume, and contains depths up to 1,642 meters. It’s about 25-30 million years old. Lake Baikal has been the home of many indigenous Buryat tribes for centuries, and populated by their ancestors and other peoples for much longer than that.
Here’s a great little article about the lake, where I got most of my info from.
That’s like, pretty deep dude.