Yes, pretty much any large duck that is white or have a large amount of white on them is domestic. I don't know of any wild species that has a large amount of white on it. Some wild species have small patches of white, but not entirely white or mostly white. All wild ducks can fly very well, too and can leave an area that they don't like or doesn't meet their needs.
I've talked to some people and a lot of it is because they can't or don't want to keep them and feel like letting them free is a good thing for them. Most people mistakenly believe that ducks can live on their own. They tell me that they see them getting fed all the time, so they know they don't go hungry. I've seen ducks starve while being stuffed with junk food. They also live a shortened life because of the food even if predators don't get them. Imagine a human eating nothing but bread, crackers, chips, popcorn, cereal all his life. By the time he's middle age (the equivalent would be about 3 or 4 years old for a duck), he would be full of health issues. That's what happens to animals, too.
Also, there are hybrid mallards, like Cinnamon in my avatar, who are also either dropped off or a result of those big domestic ducks breeding with wild mallards.
