I guess you could call them “summertime icebergs”. They’re not, of course. They seem to be made of clumps of pollen (and other stuff) that’s fallen into the lake from nearby trees. Because of the sticky nature of pollen, you wind up with these circular shapes of white and yellowish goop. Floating on the lake.
What really attracted me, though, was the visibility of the rocks on the bottom, especially while using a polarizer. For me, it created an interesting abstraction.
Now be honest: If I hadn’t told you what this was, could you have figured it out?