I fished upstream of Stillwater near the High Bridge on Wednesday evening. There was a ton of algae and other gooey looking ugly crud floating downstream. It seemed to be in a narrow band floating right in the middle of the main channel. With all the warm weather and the low water I think this stuff gets flushed out of the St Croix Island Wildlife Area and all the shallow backwater sloughs.
It does help define the current flow but it sure is ugly. I’m not sure the campers like it – I’m not sure the fish do either – I didn’t get a bite all night. If you are fishing in the goo you need to clean your line every 5 minutes or so because you get a heavy green mass on your line. 
Gross City. Here is a pic: