You have American lotus. Generally, younger plants have "pads" that simply float on the surface. As they mature with age, they will have "pads" that raised up above the water's surface. This isn't always the case, some plants seem to never have "pads" that rise above the water's surface for one reason or another. Flowers are usually a creamy yellow, but can vary from almost pure white to a bright yellow in wild forms.
The advice I gave above reference treatment holds tree for lotus. They are gorgeous native plants, but will take over a lake if not managed...
