You don't need to come to this location alone, your companions will be awaiting "outside" until you finish with this quest.
You can use Kalikke's Water Blast to free the imprisoned water elementals by shooting the 6 fires surrounding them. Doing so will give you the option to call them for help against the Gargoyle-like Treant.
There is a cave by the waterfall with a hidden entrance (Perception DC 16). In the end of the cave there is rubble that block the path, it can be cleared with Athletics DC 24 check, passing the check grants you Restoration of The Taldan Mine project.