The image and caption both comment on the flowing and cyclical nature of toxics - both materially and culturally. Materially, because the pollution is carried by a river. Culturally, because the public discourse around river pollution comes back with the seasons. Perhaps this could be highlighted a bit more in the caption.
The presence of the worker in the river also draws attention to the labour involved in dealing with toxics. The fact that it is an algal bloom as well - the presence of life - also shows how toxics are a more-than-human issue. I would like to hear more about the religous element involved in this work, too.
This picture and the caption tells us not only about the presence of toxins in the river, but also how they become visible through ecological patterns in the form of the algal bloom, and how they become invisble again through limited solutions related to social forces, such as religious practices.