Flooded Archives - Greek Fire Puzzle Northwest Corner (Part 1)

Make your way over to the northwest corner of this large area, where there's a wooden balance beam and a smaller pool divided from the larger pool by a walkway.

Move around to the room behind the pool. (This is where you found a survival cache and stack of coins earlier.)

Use a rope arrow to open the hatch...

...releasing one of many Greek fire vessels.

Stand next to it and shoot another rope arrow into either end of the wooden armature. This anchors the fire vessel to the beam.

Get another vessel out of the storage chute.

Then attach it to the other end of the beam.