It seems like the greater concentration is in the deeper water (6' or deeper) although it goes on to some degree everywhere. These are really small bubbles. I mean hard to see at all. A big one would be the size of a pencil eraser and an average size would be roughly 1/8" in diameter. I wish one of you "pondmeisters" was close enough to come by and take a look. I think you would find it interesting.......If your ever near Waxahachie or Midlothian TX please give me a call. My personal e-mail is [email protected]