Hi Katherine, wow this sound great. Here is a video I hope will help you with your project. Good luck and enjoy.
Suggested clip · 72 seconds
How to Put a Fish Pond in Your Backyard - YouTube
Building a koi pond can be easy or hard. It's pretty easy if you choose a small, pre-made pond mold and just focus your energy on water flow and how pretty it looks. My pond is an in-ground rubber lined 75 X 18 foot mammoth. (8000 gallons and 36" deep in two areas) I designed and built it myself - and did a LOT of learning-the-hard-way. The first thing you need to decide is the size you think you want and a budget. Do a BUNCH of homework way before you start. If you live where it freezes, the fish will hibernate but only if the water is deep enough (at least 3 feet) - otherwise the water will simply get too cold and the fish will die. Or, you can keep the water heated. Or, you can over-winter them in to a holding tank in a garage or something. In the south, that's not an issue. Oxygen IS an issue. The fish need plenty. The water needs to be aerated by some means and circulated in proportion to the size of the pond. These pumping systems can get complicated. It's too much to get into here. The only other major thing to consider is maintenance. You'll get a lot of evaporation when its hot and dry - so a water source is a MUST. If you have local predators, you'll also want to maintain a barrier to keep the fish safe. In order to ENJOY the whole experience from start to finish - do a lot of research first. It will grease the wheel and make everything easier. There may be a pond supply store in your area. Pick the owner's brains for information if you can - you're apt to be a long time customer!
Hi Katherine - maybe this can help you: https://www.wikihow.com/Make-a-Backyard-Fish-Pond