Low water stunt. Series of very technical rocky slides and falls.
This involves a walk-in from Boot village. Follow a track on the right-hand bank (looking upstream) out of Boot, until you reach Gill Bank Farm. Walk through the yard, cross the bridge and follow the other riverbank up to a waterfall which you can start above or below. Get out in the village of Boot itself.
Rainchasers is best experienced as an app.