Hard to really tell from that picture but I believe that is a Nutria.
@Theoldman : This was my first thought. It's whiskers do look more like an otter though in the pic.
Funny story...I was at the Houston arboretum and a nutria had crawled out of their pond onto the grass. Dozens of people, many foreign, ooohed and aaahed at it. They gathered round and took pictures.