Henry’s piccolo mistero
The unusual shadow is small and near the center of the photo. An enlarged portion of the picture is shown below:
The shadow is marked #1 - what’s it a shadow of? The thing making the shadow is marked #2. Look at the enlarged view below.
A water spider is casting the shadow — but in addition to its body, the dark “ovals” are actually caused by indentations in the surface of the water at spots where the legs are pressing on the surface! Cool! Thanks, Henry for this great find!