A pond will become a stagnant, algae-filled eyesore if you don't keep its water moving and aerated. Here are three ways to stir the pot:
Water shooting up from the surface of the pond or flowing from a man-made ornament is visually compelling and nice to listen to. Available in a variety of sizes and shapes, each linked to a particular pump capacity.
To create the show you want, measure its width in inches at the point water spills out. Multiply by 50 if you want a trickle of water, by 100 for a sheet of water, and by 200 for Niagara Falls. The result is how many GPH your pump needs for the falls alone, not counting the pond.
An air pump, a separate device from a pond pump, produces bubbles that subtly ripple the pond's surface.