Muskrat

Muskrats are medium-sized, semi-aquatic rodents found in marshes, ponds, and slow-moving waterways across most of North America, and at a glance they can pass for a small beaver. The tail gives them away — long, thin, and laterally flattened, moving in a snake-like fashion through the water rather than paddling like a beaver's broad, flat one. Muskrats build dome-shaped lodges from marsh vegetation or burrow into stream banks, and the name comes from a musky secretion they use to mark territory during the breeding season.