It certainly is *the* lake on earth.
I‘m always a bit torn on the natural wonders though. Some I consider really wonderful and unique (e.g., Mount Roraima) or unique through the interaction with humans (e.g., Mount Kaliash) others are just… one of many possible options or not that wonderful
Especially for lakes, the latter seems the case. Lake Baikal is a natural wonder in the real world, but in civ it wouldn‘t really stand out compared to other lakes with a more special „look“ or „surrounding“ I fear (Lake Hillier, Kilimutu). The way to make it unique would be the number of tiles it occupies.
On that note, we could also have the Aral Sea which starts with 3 tiles and loses one per age…