Submerged plants are often referred to as water weeds. There is nothing pretty about these types of plants, but they are the hardest working of all plants in a pond. Their stems and leaves are submerged, and they are found in the deepest part of the pond. Crucial to the ecosystem, they oxygenate and filter water, absorb nutrients, reduce algae, serve as protection for baby fish, and provide shelter for spawning fish. Stocking density is typically one bunch per 3sq.ft. Submerged plants are rapid spreaders and will eventually become invasive. If grazing fish do not keep them in check, prune them back in fall.