Koi can get sunburned!
They need plenty of shade to get out of the sun. Pond Plants help a lotwith this, so do flat, floating Pond Decorations.
Pond Fish diets need adjustment in prolonged hot weather:
In Water Temperatures up to 88 degrees feed Vegetable based (also called fall/winter) foods.
In Water Temperatures above 88 degrees all feeding should be stopped.
The ability of very warm water to hold oxygen is greatly reduced and supplemental air may be required if there are larger Koi present or the Pond has a high number of Pond Fish in general!