I am playing a game where there is one large continent, and several lakes which each have a small island with some resources. The AI (barbarian) built ships and colonized one of the small islands. It built ports at all available locations, and also some towers and a fortress, which combined occupy the entire island. How can I attack it? I also have a port on the same lake. I have a ship, loaded for an expedition, and now waiting in front of that island such that several buildings are in active visual range. I have soldiers in the port (in its 'warehouse'), and soldiers in a fortress of my own at the shore. I have a 2nd ship too, which isn't doing much...
Screenshot here: http://s8.postimg.org/u08mn4aud/Screenshot.png
Somehow I feel like that should be enough, but clicking on the tower of the enemy doesn't allow an attack. Am I doing something wrong, or is attacking across water not possible yet? (In that case, all one needs to do is conquer an island to at least get a draw in a game of autocrat?).
I'm playing bzr7686-201601031816 (a daily from 1 week ago).