Almost looks like a large, slippery hand, just getting a hold.

Tsunami? not just a rough sea

as #2 says, thats a bit more than just "rough seas". Rough seas don't come out of the blue, you will always see a graduate change on the ocean as the weather changes. This looks as said more like a tsunami or a wave from a landslide or similar. (unless the title is a metaphorical one, in that case yes, the sea can be rough )

Sometimes ahead of a tsunami the sea retracts before it gives full force and hits land. I doubt this is the case here.

...and then they washed away.

Looks like it may be a tidal bore. Looks like a river rather than a sea to me.

Looks like to me that these here tourists don't know there sea from there elbows. I bet all the locals were up in their bedrooms pissing themselves watching all these clowns getting all wet and washed away like

I think #6 is correct about it being a tidal bore on a river. @ 0:5 - 0:10 you can see buildings in the distance on the far shore.

Haha ! At start I thought the guy was right to stay on his scooter so he could have escaped a possible wave going over the fence, but then...

Where did those seven years go?