Fish pond mystery

We have a small fish pond in our garden that has been home to some goldfish for about 3 years. We didn't spend a lot of money on fancy fish like koi - these were simply pet-store goldfish. But they thrived. There are lots of nooks and crannies for the fish to hide from preying raccoons, and there are lots of bugs and organic matter to feed on. We started with a dozen fish, and they bred. Some of the original fish got to be pretty big. They survived in our pond, winter and summer, for three years.

So it was very dismaying - and puzzling - to come back home from our two-week vacation to find our goldfish floating on top of the water, very dead. And no sign of any other living fish in the water. What happened?

Yes, the water level had gone down quite a bit while we were gone - had it been terribly hot? Yes, our fountain, which provided a little aeration of the water - had stopped, too, its pump motor clogged with organic matter, its filter missing. Had a raccoon gone fishing and snagged the pump, pulling off its filter?

Is it possible that the combination of decreased water volume, heat, and no water movement caused some kind of environmental change in the pond to kill the fish?

The flowers in the pond seemed fine. The tropical water lily had four blossoms. It seemed healthy.

OK - so I got a new pump motor for the fountain. And we went to Petsmart and bought another dozen $2 goldfish.

Let's see how they do.