Otters are an aggressive animal, with an aggressive appetite. They typically travel in large groups, groups of 6 or 8 are not uncommon. Because of this they can empty a stocked pond rather quickly.
They also make "toilet areas." These are places where they go #2 every time. These are places usually surrounded by water such as sharp points, boat docks, etc.... They'll also tear into fish baskets looking for an easy meal.
We're well equipped to take care of your otter problems.