Find a way to the top of the waterfall is an optional mission in Ratchet & Clank, taking place in Jowai Resort on planet Pokitaru. Though it is immediately available, the O2 Mask should be acquired first by completing "Clean up Amoeboids in Pumping Station".
To access the waterfall, start from where the ship lands, and take the path down to the boat where you followed Felton Razz in "Find the technician". Instead of using the boat, jump into the water below, dive, and then turn left until you see a large stack of exploding and metal crates in front of the entrance to a cave. Destroy the crates by touching the exploding crate and swim through the cave, then jump out the other side. Jump on top of the rocks to the top and you should see in front of you a group of darters and a versa-target for the Swingshot. Kill the darters and Swingshot across the first gap, then Swingshot across the next.
Here, you will find yourself on several rocks on a waterfall. Climb up the rocks and head up the linear path, killing darters, puffoids, and toxic crabs along the way. Eventually, you will reach the top. Defeat the puffoids here, and a telepathopus will appear. Defeat it, and you will obtain a gold bolt.