Yikes, the swamp certainly doesn't seem very hospitable.
The sealed gate near Andergast was inside of a hollow tree; maybe the gate we're looking for is inside of this hollow tree?
Geron still can't swim, so we'll need to create a bridge out of something long that can support our weight.
Something natural and sturdy.
You'll need to do some chopping to get it where you want it.
Use your hatchet on the tree trunk that's left of the hollow tree.
You can then use it as a bridge.
As fun as it would be to jump down there face-first, you'll need a rope to get down safely.
Thankfully, our boat has one.
What could possibly go wrong?