Add’l info to discussion: “Bubbles” has been a loosely applied term here. The nature of these events are more of a “gas venting” through a sediment/aggregate material. This creates a much different formation condition than a singular type of a large spherical air cavity (or a simple large “bubble”). The air will froth in a complex gas release.
Another important note: Keep in mind the scale. The Emergency Spillway is very large. To determine the radius of a surfacing/surfaced “air froth”, it should be compared to the large size Emergency Spillway Weir to the right (near 53 feet from water edge face to backside concrete extending “foot”).
I do not believe those are bubbles. The surface is completely undisturbed. If these were bubbles, particularly if they were large bubbles, there would be some surface disturbance.