That leak around the pipe concerns me. Water moving through the dam by any means other than a pipe is troubling in my opinion. Are those rocks visible in the photo throughout the dam itself, core and all?

That does look like duckweed to me. If so, it most certainly can cover the entire pond surface, given time.

"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.