Caspian Sea

It has a diverse ecosystem.

An excerpt from the article 23 facts about Caspian Sea
Over 2,000 species live around the Caspian Sea, and approximately 400 of them are endemic to this unique area (such as Horsfield’s tortoise, Caspian gull, Caspian white fish, beluga sturgeon, Caspian turn, Caspian seal, or the spur-thighed tortoise).