Erik lives in Oregon and he restructured the interior of his pool using sand bags, soil and a pond liner to reduce the water volume and to make shelves for plants. His goal wasn't to swim in the pond but I found his page the most helpful in terms of construction ideas, photos of the steps and information on how to build a bio-filter (more on that later).
Armed with this information, I approached Jim with the great news that we were converting our swimming pool to a swimming pond! You can imagine that a man who had just spent the last several weeks painstakingly working to make your pool water look the exact opposite of a pond, in the ferocious Texas heat, wouldn't think too highly of the idea. But my husband is a reasonable man. He also knows that I can be a bit mule-ish when I get a (brilliant) idea into my head, so he read the websites I sent to him.
He stopped adding all chemicals to the pool the very next day and we continued our research. We needed to learn about water plants, bio-filters, fishies compatible with Texas weather and pond pumps.