The stuff that appears on my concrete stairs leading into the lake certainly has the qualities described in the link. It's not as dark as shown in the photo but is slippery when wet and not slippery when dry. Hosing it down does not remove it (though power washing does) but it doesn't leave a sheen in the water (like I'd expect some oil based gunk to). You can scrape it off somewhat when dry but it's a bear to do. Interestingly while my stairs have the stuff, it's only above the water line and within the splash zone, it doesn't accumulate on the dock pilings or dock which also get splashed. I wouldn't expect oil residue gunk to be so picky but I guess the algae critters are.