How does an otter’s flattened tail help it swim?

An otter’s flattened tail serves as a vital tool for aquatic locomotion, helping to propel the mammal gracefully through the water. Along with their webbed feet, otters use their tails to navigate and generate the necessary thrust for swimming.12

While river otters utilize their long, pointed tails and all four paws to swim, sea otters rely primarily on their shorter, flat tails and two back paws for movement. In many aquatic mammals secondarily adapted to water, the tail becomes a key locomotory device, and its flattened shape is an evolutionary adaptation that enhances their ability to move effectively in an aquatic environment.34