We had the same problem here on two separate occasions with beavers. Those big rodents absolutely deforested our place and kept building the natural pond dam up so high we were worried about flooding. I got real tired tearing up their dam every day, only to find it rebuilt even higher the next.
Since we moved here from LaLa Land, I didn't want to take the ultimate sanction if I didn't have to. I called the game warden who told me that I couldn't just trap and move them because they were a pest and that I had two options: Live with the beavers or kill the beavers.
About three years ago, when I spotted a big one towing what remained of my favorite weeping willow across the pond, they sealed their fate.
From that day forward, my son and I began carefully hunting the pesky critters. Beavers are quite skittish and will dive at the slightest provocation. Since they swim with only their head showing and since they are out mostly at night, that makes for a tough shot. Eventually, one got careless and made a foray out just about dusk. We had our sniper team out in a flash and got him with a .22 rimfire LR from cover as he was nearing the bank. [peep]
We got number two a couple of weeks later at night, using the big spot from my truck for targeting, but with .22 subsonics so as not to excite any neighbors. I got the third with a subsonic about eight months ago. It appeared to be a solo yearling looking for a nice place to set up housekeeping.
I suspect we'll have more. We aren't that far from the river and the young ones migrate up the streams looking for a new home every year.
If otters hit us, they would find our pond like a smorgasboard with all the bass, crappie, and bluegill in it. Plus, they move a lot faster than beavers, making for a tough shot.
Good luck.
[sniper]