Air bubbles flowing under ice can be mesmerizing.
When a thin layer of clear ice forms with a little bit of flowing water underneath, trapped air also flows along. The bubbles form and gather together at obstacles in their path, form bigger bubbles, break up again change shape as they flow under the ice.
The best time to witness this phenomenon is in the fall or spring, as it is best observed over a few inches of gently flowing water. In midwinter, the shallow water is completely frozen and covered with snow.