Haven – “Do not tempt the desperate” [Campaign 3, Mission 3]

I really don't understand how to proceed. I can't cross the water, and I'm exhausted from fighting off enemies. I've explored and cleared everything on the left side of the map. As a result, I can't enter the tall tower with the gates, and I don't know how to open them. I've obtained the Tear, but the second side quest isn't being completed, even though I've rebuilt all the sanctuaries.

How do I open these gates?