Elgand
The elgand was a majestic but elusive creature with an excellent camouflage trait. The cloven-hoofed equivalent of a hermit crab, an elgand would collect dirt and vegetation on its back and antlers. They built up these artificial landmasses on their backs to hide themselves while they grazed on aquatic plants in lakes. Elgands were commonly mistaken for islands.
Over time, the vegetation on their back would begin to grow into self-sustaining plant life. Older elgands could have two or three full trees growing on their backs. Trees could be problematic for elgands if the branches became intertwined with its antlers.
While elgands grazed, they moved slowly across the lake looking for fresh variation, causing the islands they may have been mistaken for to move. Elgands moved rather slowly and were very good at being mistaken as landmasses. The usual method of discovery was by people saying "I could have sworn that island used to be over here". Their existence was more or less a fairy tale, and though they were confirmed to be real, most people wouldn't believe you if you told them you'd seen one.
As mammals, they give birth to live young--though a common misconception among the Legerian public is that they laid eggs.
Though elgand could be found across Legere's colder north, they were especially prevalent in Lake Brokefang.
Hugh Manson of Hoobank
According to my father, moving islands is in fact the result of the activity of underwater moose that inhabit most of the lakes and rivers in the countryside. You know if a lake has underwater moose by the huge white or black eggs they lay all over the farm fields throughout summer and autumn."