I think on a similar scale would be the Chinese South–North Water Transfer Project , which has taken several decades to eventually move 44.8 cubic km of fresh w

I think on a similar scale would be the Chinese South–North Water Transfer Project , which has taken several decades to eventually move 44.8 cubic km of fresh water via canls/aqueducts etc through some mountanious terrain. Or the undground Great Man-Made River Project of Libya moving 6.5 million cubic meters over 2,820 km. Main issue ther though is the first is from already present freshwater sources and the latter from underground aquifers. With both having been done over multilpe decades to reach that capacity. Finding the water to move would be the main challenge, een though the Caspian is less saline than ocean water - there are probably water usage agreemets with the neighbourign countries preventing a massive undertaking of such size.