Your picture below looks like a bluegreen algae bloom to me. The stuff in the picture eventually works its way to the surface as the algae cell/colony buoyancy increases and forms green films as in one of your pictures. This surface scum/film resembles a typical nuisance bluegreen surface scum to me. If it was my problem, I would be intensively spraying the accumulated films with an algaecide. I would choose an algaecide that matches or corresponds to the goals for your pond. Some prefer copper based algaecides while others prefer a hydrogen peroxide (hydrogen dioxide) based chemical (Sodium Carbonate Peroxyhydrate 85%) - example Green Clean Pro.
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