I’m in the do not underestimate the otters camp. I ran a trout farm for over a decade, and otters were a daily fact of life. The largest that was trapped out was 6’3” nose to tail.
My two dogs could easily deal with a young-ish otter on land, but a six footer in water? Forget it. Plus, I rarely saw just one otter, it was usually a family group. But, boy, if they ever did find one alone and out of the waiter, it was ON.