This is a skill point.
This is a pain to get, because of the fish that eat you in the water (if you attempt before completing the level, which you shouldn't be doing). Complete the level first and then the fish won't be there. The crates are scattered all over; some are close to your ship, others are further away to the left of the area. Swim towards the TNT crate to initiate the explosive sequence, this will destroy all the crates in that collection. There are 3 collections near the ship. Once all those three are destroyed you will want to go near the waterfall which isn't too far away. There is the final collection here, do the same as you did previously to destroy them. If done correctly, it will say you have completed a skill point and the trophy will unlock too.