Otter are semi aquatic mammals that belong to the weasel family and are noted for their playful behavior. The otter has a little and slender body with short legs, a strong neck, and a long flattened tail that helps propel the animal gracefully through water. Swimming ability is further enhanced in most species by four webbed feet. Two species are marine with the others living predominantly in fresh water. Otters range in size from 3 kg (6.6 pounds) in the Asian small-clawed otter (Aonyx cinereus, formerly Amblonyx cinereus) to 26 kg (57 pounds) in the giant otter (Pteronura brasiliensis) and 45 kg (99 pounds) in the sea otter (Enhydra lutris). Fur color is various shades of brown with lighter under parts.

 Nearly all species of otters face increasing threat as urbanization and logging continue. North American river otters (L. canadensis) are still taken as part of the commercial fur trade, but the primary threats to others are the destruction of wetland habitats and pollution. Heavy metals and contaminants such as mercury and PCBs accumulate in otter tissues and in time impair both reproduction and survival. Pollution also affects fish populations on which otters often depend. Conservation of remaining wetlands and restoration of water quality are currently the most important steps toward ensuring the future of otters.

The presence of otter helps signifies the healthy ecosystem and their conservation saves the whole ecosystem.

Reference:https://www.britannica.com/animal/otter