I have a small pond in my garden, which contains 4 fish. Is it safe (for the fish) to introduce a pet cat?

The small pond has 4 goldish in it (3 large and 1 small) and has thick trees and foliage overhanging it. I attend to it and feed the fish every day. Is it safe to introduce a new pet cat into such an environment - would it harm the fish? Is there anything I can do to prevent it from harming the fish - or do I just have to give up on the idea of having a cat?