The City of Palmerston boasts 14 man-made lakes and one natural water body that are important ecological and aesthetic assets to the community. They also provide functional outcomes such as stormwater management and water quality treatment.
The lakes are a great place for the community to meet and enjoy, and play an important part of the local ecosystem, providing habitat for fish, birds, and reptiles
To manage these ecosystems the Palmerston Lakes Management Plan has been developed. Part of this plan is a quarterly water quality monitoring program, which provides a quick snapshot of lake health and actions required to maintain lake functions. The latest Lakes Water Quality Report Card can be found here.
Weed management of Council’s lakes includes the management of a number of weeds that grow in the systems.
- Salvinia Molesta
The most significant weed for Council to manage is Salvinia (Salvinia molesta). It is an aggressive, fast growing aquatic weed that form dense mats over waterways. Council have been working closely with Northern Territory Government (NTG) Weeds Branch to ensure an ongoing successful management program is implemented and maintained.
Management of Salvinia is undertaken through mechanical harvesting and biological control. The biological control is a new program of introducing the Salvinia weevil (Cyrtobagous salviniae), which eats only the Salvinia leaves. Through a combined approach of harvesting and the weevils, and the activities of the Lakes Management Plan, the management of Salvinia will be improved and ultimately more sustainable and beneficial to the lake systems.
- Herbicide Trial
Council is trialling a selective aquatic herbicide to assist in the control of Salvinia weed in addition to the current controls comprising mechanical weed harvesting and biological control. The herbicide being trialled is 'Clipper'. Clipper is formulated and approved for the control of selected floating, emergent and submergent aquatic weeds and algae.
The trial involves targeted treatment of residual Salvinia weed post mechanical weed harvesting on some of the lake edges and the results being monitored. Pending the outcome of the trial, further extension of the trial program is planned and may lead to be 'Clipper' being routinely used to treat residual Salvinia weed post mechanical weed harvesting.
To ensure safety and protection of environmental and human health, 'Clipper' herbicide will be applied in accordance with the products Safety Data Sheet and Australian Pesticides and Veterinary Medicines Authority.
Weed harvesting is underway. There is currently a back-log of lakes requiring harvesting due to the harvester not being operational for several months. Forward schedules for harvesting only includes the next three lakes to be targeted, as it is difficult to determine the length of time needed between lakes. These lakes have been chosen according to their weed coverage, current poor water quality and potential ecological impacts from the Salvinia (i.e. effects on native fauna).
Lakes are regularly inspected and assessed for weed coverage and water quality. The schedule is regularly updated to ensure the critical areas at a point in time are targeted.
The current situation of the lakes is as follows (as of 25 November 2022)
Harvester 1 (old harvester) is currently clearing: Lake 7B,
Harvester 2 (new harvester) is currently cleaning: Lake 5
Lake 1B being cleaned on weekends.
Next lake to clear: Durack 7A, 7C
*subject to change based on factors including, weather conditions, machinery maintenance, staffing etc.
Please note, lakes harvested may not be fully cleared of all weed material. Timeframes are approximate only, this information will be updated as additional lakes are being treated.
In addition to managing and cleaning the Palmerston lakes of Salvinia weed, lake management and maintenance works include but are not limited to:
• weed spraying and management of aquatic and terrestrial weeds other than Salvinia,
• maintenance of fountains and lakebed aerators,
• sediment trap maintenance,
• maintenance of reeds and other lake-side vegetation to maintain balance between stormwater retention and water quality treatment, amenity, recreational and aesthetic values and uses, and wildlife habitat.
Sanctuary Lake C (bottom lake)
Durack Lake 9
For more information about City of Palmerston's Lakes Management Plan, press play on the video below.