Coypu, or Nutria, are furry rodents looking similar to a beaver, except with a rat tail. They are South American creatures, but were transported to the US years ago to compete in the fur market. Apparently the Nutria fur never became as popular as the beaver, fox, raccoon or mink, and as nutria farms became less profitable, many of these river rats were released into the wild.
Unfortunately, they breed quickly, displacing native animals. They are environmentally destructive, burrowing into river banks, causing erosion, destroying aquatic vegetation, marshes, and irrigation systems. They chew through wooden barriers erected to house gates to control water in some of the lakes at the Ridgefield National Wildlife Refuge, causing the need for constant repair of the wetland habitat.
I see them often at the refuge, but only once have I seen a white one.