When I was growing up, every Spring and Fall, a pair of Malard ducks (a male and female) would stay in our in-ground pool for about a month. It's quite common in this area, and our neighbor had their own pair that would stay in their pool. The first year or two, they were a little nervous about getting too close, especially because of our dog, but after that they became more and more relaxed. Eventually, they knew they could trust us and even our dog, who often ignored them. We could walk right up to them, and they seemed to recognize us. One year we saw that the female had laid some eggs, but, unfortunately, a raccoon got to them. They came back every Spring and Fall for at least ten years, until my parents sold the house about 3 years ago. I'm sure that they still return there every year.
Steve