The correct response is:
"because the pond is a different material than the air, and sunlight gets refracted as it travels in and out of the water."
When light passes from air into water, it bends (or refracts) due to the difference in the density of the two mediums. This can distort the appearance of objects viewed through the water, such as the duck's body, giving the illusion that it is detached or distorted when observed from above.