we are talking over 330,000 gallons. this is a lot of water. a lake aerator might be a nice purchase during the summer months when no fresh water is being added. Its a floating pump that creates a large foaming fountain in the middle of the pond and keeps the water well oxygenated.

In a pond that size you can have koi if you want, but I doubt you will ever see them. I assume that this will not be lined with any sort of rubber liner or cement, correct? It's way too much water to try and circulate and filter so odds are it will always be a bit greenish and murky and you will only see a couple feet down. That is unless you install the mother of all filter systems. I would suggest creating some beach areas only 2-3 feet deep and always feed in the same location during the same time of day. the koi will hang out around there during feeding times. You could put 50 fish in this pond and never really worry about filtration.

you can grow lilies and marginals, but the koi will dig through them....that's what they do. but if well established in the ground the roots will come back and they should do just fine.