Unable to build dock?

I am playing as Sumerian, and I am trying to place a dock, but whatever I do I cant build one, I have tried to place it on every single tile around my island, as close to shore and as far away as possible, I have restarted the game, nothing I do will let me place down a dock, I dont know what I am doing wrong, is it a building that needs to be close in order for it to work? Also I am in the bronze age and have farms if that matters.