They swim around with their heads under water looking for food and when they see something they like, they dive. You never know where they will pop back up to the surface. Sometimes it's right near where they dived and other times it might be 30 feet away.
Here is the female with her spiked feathers.
I really like the shaggy "punk" look of these ducks.
Here is the male. You can really see how long his body is.