If your talking about the crystal that you shoot with the arrow to lower water I did that. Now that the water is down I still can't go very far, only to the room with the chest. This is where I'm stuck. Am I missing something? Is there something else you shoot?
With the water lowered follow the lower path until you reach a room with a Shutter next to a bed of spikes. Go east and shoot the crystal and the water will raise. Then, backtrack all they way to the treasure chest.



