Small Backyards can have a koi pond too - 2,000 Gallon Pond 

I had the opportunity to meet Steve Walker (of Sacramento Koi) at his home 18+ years ago. He was (and still is) truly knowledgeable about koi ponds. The design of the pond, location, expectations, and filtration planning will dictate whether the final design is a success or not. A great koi pond will have a tapered bottom and a drain for the waste to go. Some of the waste can be captured with a skimmer (leaves and debris caused by the wind) before it sinks to the bottom. The pond should have water return jets to get the water pushing towards the skimmer. Their bead filter design is very well designed, and the use of a UV light to kill the algae, get it to clump, and captured in the bead filter. The short time spent with Mr. Walker and his willingness to hand draw a design for me was solid gold. Algae thrives in sunlight when fish waste is abundant, low oxygen levels, excessive feeding. I ended buying some parts to build my own pond with the information he had given me.

what lol that's small asf