HOW MUCH DAMAGE CAN OTTERS DO TO THE FISH IN A FIVE ACRE LAKE STOCKED WITH BASS AND BLUEGILLS?

I suspect that they will stay around as long as the catching is easy. I have 2 ponds, the smaller one being close to a feeder stream known to have otters. Last year a pair "found" my small pond (3/4 acre) and ate everything bigger than 6 inches in a few days. Fortunately they didn't go upstream to my big pond, I have enough trouble there with Herons and Cormorants. Aggression is probably a good idea, at least to make them feel unwelcome.

Otters can do big damage to fish populations. Encourage them to move on.

Keep in mind that Otters are migratory in terms of their feeding habits. If there is an easy and plentiful meal they will take it, they will leave when the supply has dwindled. They also know enough to come back. Bob's version of 'encouraging' them to leave may be a little different then mine, but I think you get the idea.

I would agree that you need to be sure that you convey the message that they are not wanted in your ponds! They can do a tremendous amount of damage to your fish population. Nothing that a 3 cent projectile can't solve or a local trapper with a permit would be a better solution.