Question
What do we need to know about winterizing a pond with waterfall that contains fish?

Answer
Hello Candise!
Winterizing a pond is a bit of a lengthy subject, too long to cover here.
I can direct you toward a great (and FREE) resource, though:
Just go to www.pondmarket.com and download the free ebook:
"How to winterize the Pond".
It goes through the process step by step.
Best regards
Brigitte