This only runs when the snow is melting, so get there quick. The entrance is a ramp, with a couple of large stoppers to avoid at the bottom. After that there is a short section of boils and wavetrains. Apparently, the higher it is, the better. Stop in the eddy on the right, walk back up and do it again.
To get there; Turn off highway 17 onto Lochwinnoch road, just south of Renfrew. Turn left onto Thompson road after about 2 km, on a right hand bend. 6 km down this road there is a green and yellow painted, locked gate on the left, just before Early road on the right. From the gate, follow the sound of running water. If you cannot hear the river, then you are in the wrong place, deaf, or the river is still frozen.