It Must be Spring.

 It must be spring in Victoria as the frogs are busy breeding and laying their eggs in these frothy masses. The particular species of frog that makes these egg masses has several names, but the one that is most evocative is the PobbleBonk frog, so named for the call that they make.

A single frog call sounds like 'pock' but lots calling at once give the 'pobble' sound.

Below is a picture of the frog, courtesy of Wikipedia and you can get more information Here