From the block in the middle of the stream, take a running jump to grab the angled rocks on the other side (1). Shimmy to the right (2), pull up onto the flat ledge (3) and climb on the block on the right hand side (4).

Having the stream on your right, take a running jump to the angled ledge ahead (5). Use the triangular ledges to the right to reach the back-side of the slide (6). Push the button to open the trapdoor back where you started the level.