Please see the photos at the top of this post...they are from my pond about 1.5 months ago. You can see how this stuff makes it up to the surface. I wouldn't say it floats up, but once it gets exposed to sun, it dies and becomes brown goo.

http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Main=11412&Number=130706#Post130706

Thanks,

Darryl