This is a wildly growing biofilm reflected by the water surface (is the water surface seen from the other side still the water surface?). The water it is growing in is very clean, so these microbes are actually good guys:
I started my working life as a film maker. Then I began to feel useless and became a scientist instead. I love my new job but I can't give up cameras completely. Now I have accumulated so many photos that they're quite squashed in their digital box - so please click on them for instant liberation. If you want to know what cameras I use you have to click to see the complete profile.