The amazing real time video shows the 777 scooting along the surface of the bay for some time before impacting the sea wall.
Mary,
I think the white cloud is not water, but dust and smoke from the runway.
The aircraft hits the seawall at 00:16 in the video and the white cloud starts immediately. The pirouette starts at 00:26 and the white cloud turns red as the aircraft leaves the runway and ploughs through the dirt.
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PS The video looks as though it was taken from Bayfront Park, where I have also taken pictures. Look up Bayfront Park, Millbrae, CA on Google Maps to see the line of sight to the threshold of 28L.