Fortress Beavers are a species of beavers that grows to monstrous size. Aside from their size, nothing un-beaver-like has been reported in the story, and no special powers or abilities.
They are roaming the Floodplains near Liscor, where they are also hunted by Drakes for their meat and their pelts. They also fall prey to Shield Spiders and other carnivorous species in the Floodplains.
They are not a solitary species, but live in groups or families. While they are not shy, and attracted to anything large and made out of wood, they are not an aggressive species, unless something damages their dams. These fortified dams are however known to be a problem when they are diverting rivers. This can become a serious problem in Liscor in the rainy season.
- Mrsha on her big adventure encountered a colony of Fortress Beavers that suffered a Creler attack. When Mrsha led Shield Spiders to the spot, the animals fought together against the existential threat. When the adults learned of Mrsha's adventure, they were not amused - and Moore, very fond of furry animals, forbid them to hunt the beavers.