This video has been around for getting on for 2 years. It was extensively commented upon on the Supercub.org site for one.
The extra details given there were pretty damning. It happened at Lake Hood and the video cameraman was from memory on the south side of the lake where the water runway proper starts.
The pilot had aready totalled a C185 on floats under similar circumstances - which lead to a lot of dicussion about banning 'overpaid' doctors from flying!
Pilot DAR makes the essential point - he never got onto the step and with the wind from the west it was turning the aircraft towards the south shore and away from the runway due to the heels of the floats dragging and moving the centre of resistance aft. (the run starts from the north side of the lake so cross wind)
Fascinating background to the Beaver's design which makes perfect sense.