Weed identification is important in the care and maintenance of any pond. But more importantly realizing the potential of a plant to become a weed can assist in the prevention or minimise the risk to the environment through careful management.

As Australia's largest wholesale producer of waterlilies and other pond plants, we are the industry leader. As such, we are recognised as the main source of information, that people look to, for guidance. Oz Watergardens is currently working with the Nursery industry and the Government departments to update the aquatic weeds database. We are working together to help people understand how to recognise aquatic weeds and what they should do to help control the risk of potential aquatic weeds.

Aquatic weeds are classified according to 3 catagories.

• Declared noxious weeds,
• those that should be discouraged and
• those that should be monitored as potential weeds.

The potential of any aquatic plants to become aquatic weeds can vary greatly. Some produce an abundance of seeds that are easily spread. Some are such vigorous growers, that they choke out all other plants. While others, are only aquatic weeds in specific areas but not others.

To highlight this, let's look at Water Hyacinth (Eichhornia crassipes). This plant is a "Declared Weed" throughout all of Australia and has on occasions cost a lot in both money and resources to bring it under control.

Why is it declared a weed? Water Hyacinth grows vigorously in warm nutrient rich water. It has been recorded as one of the worst weeds in global history. There have been many examples, where this weed has spread hundreds of kilometres in large river systems.

The plants float on the water surface and continuously produce new plantlets that are attached to the original mother plant. This method of growth results in large mats that have grown so thick that they choke and block entire rivers, making them impenetrable to even the largest of boats.

When the water surface is covered with such dense vegetation, many problems occur. The health of the water is reduced through less oxygen being available and significant changes to the water chemistry occur through their high nutrient uptake. Aquatic life in the water struggles in the poor quality water. Bird life cannot feed. Mosquito populations increase. Other plants become choked or cannot get any sunlight. Decaying or dying plant material causes further pollution.

The fact that one plant dominates, upsets the whole ecological balance and can cause both plants and animals that rely on the system to die out or be significantly reduced.

Water Lettuce (Pistia stratiotes) is another floating aquatic plant capable of causing problems similar to the Water Hyacinth. However, understanding the growth habits of this plant, helps us to manage its weed potential. Water Lettuce only survives in warmer climates. This key factor, is the reason why it is not declared an aquatic weed in all areas. In areas where the Winter temperatures fall below 18⁰C for longer than a month, the Water Lettuce plants wither and die.

Unfortunately there is no one up to date website, listing all the Declared and potential aquatic weeds in all parts of Australia. Currently you need to refer to your individual state government agriculture departments. We have even had problems trying to get accurate information ourselves and even had instances where different departments within the same regions have different lists.

We hope to work with the various agencies to develop a national register of aquatic weeds, but understand that it will take time. For the moment we recommend going to the www.weeds.org.au website.  Go to the Noxious Weeds List, then go to Click here for the entire Noxious Weeds List.pdf format.

The control of aquatic weeds is a challenge, due to the highly sensitive nature of the environment they are found in. Unlike terrestrial weeds where many herbicides and other equipment can be used. The aquatic environment restricts the use of heavy equipment and many herbicides are unsafe to use near waterways, due to the harm that they cause to other life such as frogs and fish.

Algae can also be a major concern for most pond owners. Algae are much simpler plants and more sensitive than larger plants. Therefore, carefully applied, low dose algal treatments harm the algae but are still below levels that would affect larger plants. Various algal treatments and products are available. However, the best solution is to establish a healthy ecological balance in your pond. Let nature do its job, with only a little help if necessary.

Tips

For further information on algae and algae control go to our Tip and Hints page.

Declared and noxious Aquatic weeds of Australia

Further information can be found on www.weeds.org.au