Combine four photos together with PowerPoint.

The Fantastical World at the Bottom of the Stream!
Photos numbered 1, 2, and 3 in the collage are three consecutive shots taken in rapid succession, approximately within a second, capturing the underwater scenes. By observing the position of the rock, it can be confirmed that the camera remained stationary. However, the shape of the rock changed, and the patterns on the rock varied. The fish swimming by also underwent various transformations. The fish with the same number in the photos are actually the same one, allowing us to observe its rapid changes. It's truly fascinating!
This phenomenon is caused by the propagation of water ripples. Photo number 4 shows the ripples on the water surface at that time. The crests of the water waves act like convex lenses, converging the light rays, while the troughs act like concave lenses, causing the light rays to diverge. As the water waves continuously propagate and move, the rocks and fish at the bottom of the stream undergo constant deformation. The refraction of light also results in a dispersion effect, occasionally creating colorful formations on the rocks or the fish. Upon closer observation, nature always leaves us amazed.