The bottom of the feeder should be between 4-6 inches off the water. You don't want the food to get wet as the swans swim toward the feeder and cause a wake. You also do not want the feeder so high off the water (in times of drought) that cygnets or even the adult swans have a hard time feeding and can't reach the food. If the feeder is on a float, that is great as it will fluctuate with the level of the water. You just have to be careful in times of drought, because the float may sink the feeder too low and allow pests (ants) or predators (raccoons, turtles, etc.) to feed from the feeder and attack the swans.

The Regal Swan