Recreation Swim Pond (also called an organic pool):
- 6000 gallons
- overall size: ~ 20 feet x 20 feet
- shallow end depth (old koi fish pond): 18 inches
- swimming pond depth (new pond extension): 4.5 feet

Took us about 3 1/2 weeks to build it and it cost approximately $2K in materials so it's very doable on a small budget.

And yes, we do still keep koi fish (some goldfish & golden orfes also) about 30 of them in total from 2" to 12" in size and of course we swim with them:
   • Swimming with the koi fish in the rec...  

Parts & materials list:

Best work gloves: https://amzn.to/3TUKpE7

Backyard hanging lights:
https://amzn.to/33JlZCR

LED RGB Smart Lights (2 sets):
Novostella 2 Pack 20W Smart LED Flood Lights, RGBCW
https://amzn.to/3bfLekc

Wavemaker (to keep the water moving and circulating):
https://amzn.to/2T1VOFd

Patio chairs:
https://amzn.to/33vbtih

Waterfall attached to the deck:
https://www.amazon.com/gp/product/B00...

Or if you want a smaller version (this is the one we used on the forest side waterfall):
https://www.amazon.com/gp/product/B00...

Or something like this if you'd like to go in between the 2 sized we used:
https://www.amazon.com/gp/product/B00...

Deck waterfall pump (need powerful pump to push wide water blade through above linked waterfall):
https://www.amazon.com/gp/product/B07...

Canister filters (2) (on the deck waterfall and the stone waterfall)
https://www.amazon.com/gp/product/B07...

Pumps (2) feeding the stone waterfall and the bowl waterfall:
https://www.amazon.com/gp/product/B00...

Skimmers (2)
https://www.amazon.com/gp/product/B00...

Liner:
20' x 30'
https://www.amazon.com/gp/product/B00...

Other sizes:
10' x 10' liner:
https://www.amazon.com/gp/product/B00...

10' x 15' liner:
https://www.amazon.com/gp/product/B00...

12' x 15' liner:
https://www.amazon.com/gp/product/B00...

10' x 25' liner:
https://www.amazon.com/gp/product/B00...

15' x 20' liner:
https://www.amazon.com/gp/product/B00...

20' x 25' liner
https://www.amazon.com/gp/product/B00...

Liner seam tapes (to attach old pond liner to new. you need both for a good bond that lasts)
3" Double sided:
https://www.amazon.com/gp/product/B00...
6" One sided cover tape:
https://www.amazon.com/gp/product/B01...

Liner tape primer (needed to get a good bond that lasts):
https://www.amazon.com/gp/product/B00...

Flexible Tubing:
https://amzn.to/3y2mndx