I started a new save and finished the game. I definitely hadn't raised the water on my first time through, but I definitely did get up to change the door state. Maybe the way I got up there with the grapple was cheese?
I think as soon as I got there with the water not raised it took away my HUD (and all current_chips). I made a copy of my first sav, and replaced the current_chips with the values from my 100% save (when I did this I tried saving and qutting to the menu and it updated my 0% to 100% automatically). I didn't have to try very hard to get through that area again without the water raised. Where is it supposed to be blocked because of the lack of water?
Super fun game, hope to see more! Have you played Worms Armageddon by any chance (it would be fun to do some ninja-rope style swinging too)?