While this may initially look like an animal opening and shutting its mouth, just try going back to first principles.

1. The camera is pointing at the surface.
2. The sun is shining on the surface.
3. The water is moving rhythmically.
4. The object is just the sun shining on the water's surface.

Don't believe me? Have a look at the real thing from the links page on a sunny day! Unfortunately this camera is no longer operating.

Sorry, not Nessie.