Wow. Can't see the tail well, but are you sure it's not a juvenile beaver? There's LOTS of those around. Could it be a juvenile nutria?
Otters, I haven't seen many of those. Are they rare around here?
Maybe. I really don't know and I was just guessing as to what I thought it might be. This is the first time we've ever seen an animal that looks like that swimming around the lake. Next time we go for a walk maybe I'll bring my DSLR so I can get a better picture (the ones above were with an iPhone), but of course if I do that it means we won't see it!
Edited to add: I looked at both the river otter article linked above and the Wikipedia article about nutria (they call it a "coypu") and it looked like it could be either of those. The tail looked a lot skinnier than any beaver I've ever seen, but I'm no expert so I don't know.
