Why are beavers fur waterproof?

Beavers' fur is waterproof due to the presence of natural oils produced by their skin, specifically from the castor glands. These oils coat the fur, creating a barrier that repels water and keeps the underfur dry. Additionally, the dense, layered structure of their fur helps trap air, providing insulation and buoyancy while they swim. This combination of oils and fur structure enables beavers to thrive in aquatic environments.