The puddle ducks or dabbling ducks, as they are known, strain food from the surface of the water or by tipping and foraging on the bottom of shallow areas. This female Mallard (although it may also be an American Black Duck - they can be hard to separate) is swimming along the surface straining the water with her lamellae using a means less commonly seen then tipping up to forage.
I happened to see these two lovebirds one day in a shoving match. They were not fighting and there was an entire flock of ducks cheering them on. One would push the other backwards for a distance and then it would be reversed. They were mainly using their bills to push. They are American Black Ducks.
The reason I am including this photo is because you can readily see the lamellae, the comb-like ridge along the bill with which dabbling ducks strain the water. By the way, the male is on the left.
I decided to include the last photo in the series I took of this unusual incident. My guess is it was some kind of mating ritual. It is the only time I have ever seen this kind of activity. I was also in plain sight and they had to have known I was standing there. That speaks to their tameness.