Here's why:
* Food source: Walruses primarily feed on clams, mussels, and other invertebrates that live on the ocean floor.
* Physiological adaptation: They have adapted to live in saltwater environments, including a thick layer of blubber for insulation and powerful flippers for swimming.
* Reproduction: They give birth and raise their young in the ocean.
While walruses may occasionally venture into brackish water (a mix of saltwater and freshwater), they are not adapted to live in freshwater environments.