TJ, from my experience this is very likely what happened. I lost several dozen FHM that were along the surface as I was applying. I'm sure something very similar happened here. The surface water absolutely becomes a soup that will suffocate your fish if they enter it. To be honest, I'm not sure even partial treatment of a pond with only 2-3' deep water would have helped. When there is only 2-3' of depth, you are going to have mortalities with any significant amount of polymer, or at least I would think.
Another question, how is the water to air interface during application? Once you have a coat of the polymer on the surface, it seems to me the O2 diffusion would be minimal. Maybe it was as much an O2 crash as it was suffocation?
