My best guess would be a waterlily named "Bliss" A very lovely flower. The colors and petal shapes are just about right on the money.

Link to my Bliss below...

Here is a link that might be useful: {{gwi:630210}}

Does it always have the large center w/ pollen? If so it's not a waterlily & therefore not Bliss. I think you've probable gotten hold of a mass produced dahlia from somewhere like Home Depot that while pretty in the garden wasn't named other than "Dahlia". It doesn't comform to any of the regular dahlia forms if this is how it looks all the time.