One of my favorite stages from Melee, the Great Bay stage returns in Ultimate. It's based on the Great Bay Coast from The Legend of Zelda: Majora's Mask. One of the stages that is the most true to the game it's based on.
There are not many hazards per se. You fight on the giant turtle, and he does sink under the water from time to time.
The biggest danger is underneath the stage. Falling into the water isn't the bad part. It's just hard to get out of it. Making an easy situation for an opponent to get a good smash attack when you come back to dry land.
Not my favorite stage in the series, but it's up in the top of all time favorites.