The stream section starts at 21:43.
If you die or fail you'll need to restart the chapter. Reloading the last checkpoint will void the achievement.
The stream section is found at the end of Chapter 6. This section involves riding a large crate down the stream and solving puzzles to open seven gates along the way.
I have details on solving each gate in the spoiler tag below.
*** Spoiler - click to reveal ***Gate 1: (21:43)
Grab the box from the platform above you and drop it on the button ahead.
Gate 2: (24:43)
Grab the rock above you and double jump to dunk it into the tube ahead.
Gate 3: (25:00)
You'll be headed toward some spikes. Stand on the back end of the large crate, grab the box from the platform above, and quickly double jump over the spikes. Drop the box on the button ahead.
Gate 4: (25:21)
First, there are two spikes to jump over. Grab the box ahead and carry it to the next landing. Set the box on the button then drop Otto down the slide. Use Otto's shock to turn on the switch then pick him up on the other side.
Gate 5: (26:00)
This next landing is just like the last one but will require a little bit of timing. Grab the box from above and drop it on the button. Wait for the large crate to float under the switch then drop Otto down the slide. As soon as you drop Otto, start running the right side of the landing but don't forget to use Otto's shock to turn on the switch below. If everything timed out right, you can catch Otto as you jump down to the floating crate. You may need to use your double jump to correct yourself as you fall.
Gate 6: (26:17)
This is just like Gate 2 but the tube will be facing away from you and you have less time to dunk the rock.
Gate 7: (26:35)
The first jump is pretty tricky. Use your double jump at the height of your first jump to make it to the landing. Grab the box and pull it back so you can drop Otto down the slide. Climb over the slide and wait for Otto to land on the seesaw. Jump to the right end of the seesaw to launch Otto. Use Otto's shock as he passes the switch to open the gate.
The final obstacle is a crow waiting for you just past the last gate. The achievement will unlock when you walk out of the cave.