I think around here they close ponds and lakes to swimmers when blue-green algae appears. There was an article in the paper just today about a pond being closed for that reason. Perhaps there is more than one type of algae referred to as blue-green? Or maybe it needs to be cleansed in some way before its safe to ingest?
"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams