This short video of an underwater plant shows how bubbles of oxygen are created in water. The blurry picture has lost the details of the original video. Look around the center to see the very small bubbles.
The bubbles, that rise from a root, contain oxygen, CO2 and other gases that are byproducts of the metabolic Photosynthesis within the plant. The tube in the center of this video is a root that was formed by the plant as an exit for excessive amounts of gases.
The name of the plant is Egeria Densa. It has a relatively fast oxygen cycle and leaves in a cold fresh water like a lake, a river or a cold water aquarium. It is also a great oxygen generator for aquarium fishes that need a lot of dissolved oxygen.