Finale at Wild Blue Yokohama?

It looked to me like it was shot at Spa Resort Hawaiians, which is the actual place.

http://www.hawaiians.co.jp/
http://www.hawaiians.co.jp/asobu/waterpark/wp02.html

Though the two parks do look similar, and the real place has all sorts of rides and whatnot now, so I can't say for sure. They could have covered all that up somehow in the movie, though. I think it would have been too obvious to most Japanese if they filmed it somewhere else, though; this is a pretty well-known place.

I can say for sure that it wasn't Wild Blue Yokohama,
because Wild Blue Yokohama has been closed down in 2001.
It's too bad, I really miss that place.
Had lots of fun there as a teenager.