Does it look something like this? It's just starting and earlier than last year, and for me it will get worse, covering the entire pond. At it's worst, Bill Cody tested it for me last year and confirmed it was BG algae (cyanobacteria, etc., IIRC).
Too many hot, calm days (at and near 100 degrees). If like last year it will get so bad it's hard to be near or on the pond.
Nasty stuff
