Chemistry Expert on Film in Raccoon Creek Ohio from Mine Drainage

What might this film on the water be? Hi all, I'm a photographer working on a story about restoration efforts in a local river and am trying to figure out what this film on the water may be? I know nothing about chemistry and no one around me seems to know what this could be. This is Raccoon Creek in southeast Ohio, and it's a waterway that has been heavily impacted by acid mine drainage for decades. This photo was also just downstream from a limestone doser that is helping to reduce the impacts of the iron and acid mine drainage. Any help would be greatly appreciated!