It's not about the mechanics of the water transfer. About half the canal itself IS the man made lakes. The ships need to come in from the ocean, float in throug

It's not about the mechanics of the water transfer. About half the canal itself IS the man made lakes. The ships need to come in from the ocean, float in through the lock, and then continue course over the lakes. Prior to the rivers being damned to make the lakes, they just emptied into the ocean directly. No net new fresh water is being created, we're just holding it up for a bit so we didn't have to build as much canal. If anything, we're diverting more of that aater away from the Atlantic and towards the pacific than would normally have drained in that direction by doing this.