For those not familiar with the northern pintail, it is a species of dabbling duck, so called because such fowl upend on the water’s surface (leaving butts in the air). This allows them to graze beneath the surface. These ducks rarely dive. It’s of note that mallards are also dabbling ducks.
As are many other species that inhabit White Rock Lake. Like these:
Both are males (hence the curly tail feathers), but what species they are I haven’t a clue. There are other photos which hopefully can aid in that endeavor.
Just not this one.
Still, both show where dabbling ducks get their moniker.
And for those who must know, this is indeed gratuitous duck butt. You know you like it.
[Update] I have since identified the white duck as a pekin duck (a.k.a. domestic duck, white pekin duck, or Long Island duck; Anas domesticus).