This is the first time I've ever encountered one, but this one seemed almost tame! Here is the picture our friend Jackie contributed of her sighting on LB Lake: http://austintexasdailyphoto.blogspot.com/2011/05/nutria.html
Wow! A Nutria dug a hole through the dam at our creek when I was a kid. I was always terrified that it was going to get me with it's big claws, but I never actually saw one until now!