Submerged oxygenating aquatic plants are important to pond ecology. They oxygenate water for fish and beneficial bacteria, compete with algae for light and nutrition, and serve as food and shelter for fish. The general rule of thumb is one bunch of submerged plants per square foot of pond surface. Dwarf sagittaria and vallisneria need to be potted; our other oxygenators are sold as stem cuttings in bunches, and may be potted or simply released to grow submersed.