I smelled woodsmoke while swimming at the sand banks on the Grass River. At first I assumed there was a bonfire at one of the houses, but the scent was odd, and very bitter. I saw movement out of the corner of my eye: beside the remains of a fire, there was smoke coming out of the ground. The fire must not have been put out fully, because it had burrowed under the ground, burning through fallen pine needles and fine rootlets. When I found it, it had spread in branching patterns over about a square foot of ground, and it was expanding towards the rest of the forest. I dumped over 12 liters of water (carried up from the river) on it, then dug it up to make sure it was entirely out (third picture). I'm not sure how far it would have spread if left unattended, but it had already started to kill the roots of the nearest tree. Please keep fires in stone-lined firepits, and put them out completely with water when you leave!