Water lily (Nymphaea odorata).
White water lilies are common in ponds in our area;
the pink form is rarer, but not very rare.
The pink form is listed as forma rosea in
some references, but Gray points out that the white
form passes by degrees into the pink form. The USDA
PLANTS database lists this species as native only in
Westmoreland County in our area, but it is difficult
to sort out native from introduced populations, and it
can be seen in many ponds in Allegheny County.