Noki Bay is a level in Super Mario Sunshine.
Episode 1: Uncork The Waterfall
The normal blue water of Noki Bay is all purple and polluted. The elderly Noki believes that it's the corked-up waterfall that's preventing fresh water from filling the bay. Mario goes up the side of the rock wall to where a weasel in a cannon dome is situated on the cork, then tosses a Bobomb back at the weasel to defeat him and cause the waterfall to uncork itself. This will give Mario a Shine Sprite.