In article , says...

http://www.bbc.co.uk/news/world-asia-pacific-12709856

Interesting----but not all that huge. I've seen whirlpools
nearly that size in several places in Northwest---most notably at
Hole-in-the-Wall near the Octopus Islands and near Dent
Rapids. Those things are one of the reasons you wait
for slack water and plan your passages around the tide
and current tables.

Mark Borgerseon