Check the Clues - Skulls
Compare the teeth of a giant beaver and a modern beaver. The giant beaver had blunt-tipped incisors for gouging, not the chisel-like incisors of the modern beaver. This difference suggests that the giant beaver did not cut trees and construct dams to modify stream courses like the modern beaver. Still, the large size of the giant beaver and its skeletal structure suggest that it needed large bodies of water for its habitat.
Beaver Skull (Castor canadensis)
Giant Beaver Skull (Castoroides ohioensis)