Organisms can be used to help control and prevent aquatic weed growth in ponds. Biological treatments may not work as fast as chemical treatments, but can be effective and a long term solution to problems. This method works better in smaller scale applications and it is important to contact a lake management professional before introducing organisms into your pond because you could see negative effects from this. Some common biological treatments are other plant species, plant eating fish, and bacteria.
Aquatic Plants - Often times introducing more desired species of plants can assist in helping rid the pond of a nuisance species. Native plants are usually a good bet because they have more checks and balances with the local environment. This can be difficult because invasive species are often present because they can successfully out compete desirable plants. This method works better when the invasive plants are removed.
Plant Eating Fish - Introducing plant eating fish, or herbivores, can assist in limiting plant growth. Grass Carp are being used to help control aquatic vegetation. They are bred to be sterile so they will not reproduce in the pond and will eat vegetation in the pond. Grass Carp do not like all forms of vegetation and there are various restrictions on their use, so consult a local professional or regulatory agency. They also do not eat algae, contrary to popular belief, so they can shift your pond from aquatic plants to algae growth.
Bacteria - Bacteria and fungi can be used to help control aquatic plant growth. Certain varieties of bacteria and fungi live on various aquatic plants and can be used to selectively control aquatic vegetation. The attacked aquatic plants will die from the introduction of the bacteria and fungi and the more desirable plants will be unharmed.