The pilot may be skillful etc., but it is a really dumb thing to do if it wasn't for a stunt (filming etc.,) with various permissions and waivers / risk assessments in place. One slight miscalculation and they/he/her are suddenly upside down, under water, in the middle of a freezing lake, at best needing the assistance of the emergency services. But even if they have done it 100 times they open themselves up to prosecution.
Being N registered, I wouldn't be at all surprised if some enforcement action came from this. I could see a prosecution based upon:
§ 91.13 Careless or reckless operation.
(a) Aircraft operations for the purpose of air navigation. No person may operate an aircraft in a careless or reckless manner so as to endanger the life or property of another.
Especially if a passenger was carried then this would be an open and shut case in court. They often apply this to low flying type of incidents too and penalties can include certificate suspension or revocation. I am sure that in this case it would be a complete revocation if a pax was being carried.
Of course they might have been suffering from cab ice and were intending to put the aeroplane down in the lake, but then the engine picked up and the climbed out. On the climb out they had the problem again and so decided to put the plane back down in the lake, only for the engine to pick up again....
