hehe, I've come across such bubblings coming from the water too.
Back then I was a kiddo out with my dad at the reservoir and also
by the water's edge. Could see a big(i was small, i was a kiddo)
patch bubbles rapidly breaking out the water's surface and it was
approaching where I was standing. My dad told me its a school of
fishes, but I didn't wait to find out, panicked and went further
away from my previous spot and just saw the patch of bubbles move
by. 
