Go back one room (past the corridor and the water)
As you pass the waterfall, there are some spears on your right
Considering you are facing the waterfall from the point where you first came from, look to the right
There's fire hanging on the seeling
Hit it with a spear or a gun, there will be some bushes lit
Now light your spear, and throw it (triangle) through the window on the right of the waterfall, go through the waterfall yourself, and collect your spear
It should still be burning, otherwise you have done something wrong
Now go back to the room where carl and hayes are, light the bushes and I hope you can figure out what to do next yourself