I have a river nearby and on occasion have done the same, however as I have aged, I do stuff like this less and less. While I feel SOMEWHAT comfortable with keeping the plane out of the trees, I typically get more worried wondering what happens if the engine quits. Altitude is your friend when flying single engine airplanes. If it quits and the river is surrounded by trees and rocky terrain, you have zero chance of finding a suitable emergency landing spot. You either land in the shallow and possibly rocky river, or you end up in the trees.
I did not listen to the sound, but I am guessing that is an experimental RV4 or RV8 aircraft. While I don't condone low level aerobatics, the roll he did was probably not as dangerous as the extended steep turn he executed right after it. Depending on his airspeed and whether he was paying some attention to it, he could have snapped over into a spin with insufficient altitude to correct.
But hey, this guy is enjoying life and we all needlessly expose ourselves to unnecessary risks on occasion so who are we to judge.
Someone mentioned a t-34 earlier. Here is a pic of one I am doing a top overhaul on now. They are solid fun planes to fly, but they feel quite a bit heavier than what that guy in the video appears to be flying.
