I initially thought this was an algae, floating on top of the water. It may on fact be a moss. It appeared to be slimey and somewhat thick. It was also floating at the top of the water and appear to br shaped like a bubble.
Sorry for the graphic content -- I am withholding some even more graphic photographs.
Both herps lost; the frog kept puffing itself up, and the snake eventually spit it out. The frog never moved; its skeleton fell off the siding several months later.
Found it wriggling on the ground trying to dig, placed it in my mulch pile and covered it up.