Fair question.
The fire is on a small prepared bed of river sand on top of the rock.
The rock was chosen because it obviously lies under the water when the river is in spate and the fire was quite small. It looks far larger than it was due to the perspective of the 17mm lens.
When the fire burned down, the ash, a few small bits of charcoal and the river sand was all brushed into the water which was already full of rock flour from glaciation upstream.
The wood, including the piece the pot is hanging from, was all driftwood collected from the high water line up and down stream for no more than twenty metres.
When cleared up, It was hard to tell anyone had been there at all. The main sign being the lack of dry driftwood.
I hope this answers the question to your satisfaction. As a landscape photographer I too value the appearance of the locations I use and more often than not, leave them cleaner than when I arrive.