The Scuttlebut write-up says this is "blue-green" algae, which is the same stuff that was in the lake where I sail last year; and all the local health departments said it was too dangerous for swimming or boating. It wasn't nearly as dense here as those photos show, yet they were cautioning against any contact with the water. It scared a lot people off the lake all summer. I still sailed in it, but I always showered immediately afterwards.