Following Tyleer Bell's excellent directions, I went up to Rio about 1 PM,
parked on the street near the Rio Grande and decided to just scan the pond
for the BBWD before getting some lunch. I wheeled up to the foot of the
footbridge, looked down and there he/she was. Right under me. I didn't even
need to get out my binoculars. I even got to hear it whistle (actually, it
sounded more like a squeak...)

Boy, is that one beautiful duck! I like Sibley's ID comment -
"Unmistakeable." After a good lunch at Rio Grande, I went back for another
look. The mixed flock had moved to the side of the pond by the children's
play area, and the BBWD went up the bank there. I drove around to the lot
behind Rio Grande, and got to see it posing for several other birders who,
unlike me, had been smart enough to bring their cameras. It was still posing
when I left at 3:30 PM.

In the behavior department, I noticed that it seemed to follow or swim
directly at a couple of the white domestic geese a fair amount of the time I
watched it. It was following the domestics when it got out of the pond, but
then wandered away from them and cropped at some grass. It seemed to be
fairly aggressive and willing to show dominance toward the other geese and
ducks; another birder there said that it was in the thick of a squabble over
bread chunks someone was tossing from the gazebo, and even flew up in the
air after  them!