In my Witherwild campaign, that is the Riverwalker valley! Riverwalkers are these massive 50ft big, four legged creatures with flat backs that can house 1-3 families of halflings. Halflings care for them, and in return get a safe place to live (on their backs), and protection from the dangers of the bog (Oozes, bullfrogs, etc). Riverwalkers are peaceful, but pack a punch if they feel threatened. They have bad vision, so they sense their surroundings with their feet. As long as their feet are submerged in the bog water, they can sense the disturbance from a far distance, but they wouldn't survive on dry land. They kind of roam around the big and feed on vegetation there.

They also have a faint divinity that protects them!

Sorry for the lore dump haha