The mermaids are one group of these. It has been a very long time since I encountered them, and I have never had occasion to speak to them, but I have seen them and heard their music as I sail. I don't know where to direct you if you are interested in meeting them, but I imagine they will turn up if they have a message or lesson for you.
Another group of beings that I have not had personal contact with are the sea serpents. Other a glimpse or two, they have not factored into my journeys thus far. Like many beings of the Otherworlds, they have their own business to attend to.
The orbs are among my favorite beings in the Otherworld. These sentient balls of light dance and play, often in groups, over the waters and in the forests and meadows. They are joyful and peaceful. They communicate in their own fashion, and if you are lucky enough to encounter them , savor the experience.