I've got something like that starting in my pond. I was free of it until the tropical system dumped a bunch of rain on us. It refilled my pond thankfully, but I guess it also added a little extra nutrients. Mine is more tan, tho, and is starting to cover just about every plant and rock.

.10 surface acre pond, 10.5 foot deep. SW LA. The epitome of a mutt pond. BG, LMB, GSF, RES, BH, Warmouth, Longear Sunfish, Gambusia,Mud Minnows, Crappie, and now shiners!!...I subscribe!!