I think you may have nailed it
I got the impression too that it looks like a dead algae and it just floats where ever the wind takes it.A few weeks before all this started i did spray the banks with Kermax (weed and algae killer). The fish don't seem to mind it at all and the opposite end of the pond where it accumulates always looks good.For fun this weekend i might just take my pump and try to sink it .
thanks so much for your reply and i'll keep ya posted if it eventually goes away..........Larry