I don't know why, but I'm fascinated by the conditions that create this thick foam, as well as the movement and structure of the foam. The foam is very dynamic as it interacts with the water surging through the channels. And it's fun to look at the foam up-close — to see the details of the differently-sized bubbles and how the bubbles fit together, change position, and reflect light:
I haven't looked into this before, but it looks like there's quite a bit of research about the complicated behavior of bubble clusters (or the physics of foam). See here for an example from UC Berkeley.