We are on a well. I have water lines plumbed around it so accessing water for filling or otherwise is no problem. Our property is bordered by a dry creek. When we have drained it in the past, I just pump it and use the water to water my trees and vines. Then scoop the algae sludge and mix it into the orchard.
IF there is any hope of making that a "clean" swimming hole you will need to get all of the "stuff" out of it. It sure looks like a mound of dirt on the left side. With the liner sitting on the edge of the dirt hole it will be hard to keep the dirt out so you will need a VERY good vacuum. Lets see what happens when you try to get all of the stuff out and we will go from there.
While I could possibly imagineer a solution for circulation and filtration, even skimming, I think vacuuming is the biggest hurdle. The pool is big enough to make manual vacuuming virtually impossible, even if he had the time and inclination. Without an automatic vacuuming system, it’s going to be a real challenge to keep the pool bottom clean enough, which means it will be a constant battle to keep it properly sanitized. A suction-side or pressure-side vac is going to be able to crawl right up that slope and out of the pool, right? Does anyone know: is there a robot that could be programmed to stay in a pool with that kind of edge?
Until there is a solution for vacuuming, I’m not sure I’d proceed with making that pond into a swimming pool... it’d be a lot of work.