I have a pond in my backyard. Its 4 feet long, 3 feet wide and at its deepest its 2 feet. It has ledges around the edge that are about 1 foot deep. and a foot wide.
In the pond we initially put 6 little baby goldfish from Petco or Walmart (forgot now which store they came from) in it some 3-4 years ago. They were about a couple inches long and looked absolutely tiny in the pond. They have since grown into 8 inch long adults. They have also spawned several times, and despite the fry and eggs being eaten, two from each spawning season have always managed to survive.
We now have 4 more goldfish in the pond of varying sizes. 10 total. Some day we might run into a problem. In fact, now the old pump we have in there to help filter the water has broken down and it looks like we might need to get a new one. Thankfully, the weather isn't as hot as it has been so the fish don't look to stressed.
Here are some pictures. Sorry if they are too big.