Today is Theme Day and the theme, chosen by vote, is Shadows. ( Click here to view thumbnails for all participants )
I was walking along the Riverwalk in early April (shortly after the theme was selected) and noticed that the shadow in the Chicago River, created by the Columbus Street Bridge, was pretty interesting. It resembled a pool that is used for swimming races - the kind with the lane dividers. The shadows from cars, taxis, and trucks that drove over could be the racing swimmers.
Here's a side view of the shadow and the bridge that created the shadow. Plus there's some bonus shadows: the railings from the Riverwalk create some geometric shadows along the sidewalk.