Castlevania: Symphony of the Night

Tap or hold Y on top of the water as the wolf. It's cute.

In order to swim safely, you will need to have the Holy Symbol relic (or "Holy Snorkel" as some like to call it) in your possession. (This can be found in a hidden area in the Caverns, and you'll need the Mermaid Statue in order to access the room in which the Holy Symbol is found.)

As a wolf, when you are in water, press and hold Y to make Alucard swim upward. Press left and right to move in the desired direction when swimming. If you let go of Y when swimming, you will sink, but you can still press left and right to move about when descending.