Can Koi be kept in a pond that contains plants?

One again, millions of healthy and happy koi living in plant infested ponds are proof to the contrary
Koi and plants actually complement one another in nature, as they do in ponds.

Koi are happier and healthier when they are kept in the most natural setting possible.

Why would any water gardening enthusiast ever argue with Nature?

The aquatic circle of life is absolutely the central concept of ecosystem ponds and fish are one of the essential ingredients in that infinitely rotating circle.

Not only can they be, but koi should be kept in ponds that contain plants. For more information visit Platinum Ponds.