Australia, New Zealand & the South Pacific - snorkel around New Zealand

I got one of the UA fare to NZ in Jan, thanks to FT. I will be there about five days. Landing in Tuesday noon and leaving on Sunday morning. Is there a good beach I can go for few days with great snorkeling from the beach?
Is Bay of Islands good choice?
Thanks!

There is a place on the way from auckland to the bay of islands called goat island which is ment to be good to snorkel its near the northern boarder for of auckland.

I've heard that the water is quite chilly. True??