Forest Lake management plan

Council is implementing long-term solutions as part of the Forest Lake management plan to improve the health of Forest Lake for the community and the environment.

Brisbane’s natural environment makes our city one of Australia’s best places to live, work and relax. It’s important that we continue to work together to protect our waterways to ensure future generations can enjoy them.

Council is investing more than $1 million over two-and-a-half years to implement a long-term plan to combat the ongoing issues affecting Forest Lake.

This program is in addition to a range of other measures Council is undertaking to improve the health of Forest Lake.

Summary

This table provides summary information about the Forest Lake management plan including address, ward, project outcomes and latest update.
Address The Lake Parklands, Forest Lake
Ward Forest Lake
Project outcomes To reduce algal blooms in Forest Lake and improve the health of the lake ecosystem
Latest update

Project background

The lake at Forest Lake is a man-made wetland that was originally designed as a stormwater quality improvement device to:

  • improve water quality flowing into the downstream creek system (Oxley Creek)
  • provide recreational and visual amenity for the community.

A number of environmental issues have affected the lake over the last few years including:

  • blue-green algae growth, creating poor water quality that can cause skin and eye irritations for people and pets touching the water, as well as emitting a strong musty odour
  • extreme growth of the water weed salvina, which is highly invasive, can cover the whole lake surface and reduces oxygen levels for fish and other aquatic species, resulting in the death of the pest fish, tilapia (cichlid fish) and small numbers of native catfish
  • the ibis populations increasing on Bird Island and other areas around the lake, resulting in odour issues and high nutrient levels in the lake.

There is no one quick fix to solve these environmental issues at this man-made lake. Improving the health of the lake ecosystem will need a range of solutions and will take time.

About the project

A two-and-a-half-year program is underway to improve the health of Forest Lake. This includes the following measures to reduce sediment and nutrient levels in the lake and enhance water movement. These are key elements in reducing the conditions that support algal blooms.

  1. Development of a strategic management plan for the long-term management of the lake.
  2. Desilting the lake to remove large volumes of sediment and nutrient loads that have built-up over time.
  3. Replanting with aquatic macrophytes to encourage the return from an algae-based system to a plant-based system.

While these measures are being introduced and until the ecosystem health improves, the lake may see further occurrences of algal blooms and salvinia growth.

Download the:

Project update - early 2020

Lake update  

In recent weeks we have been experiencing some rainfall across Brisbane, as well as high temperatures. One of the greatest impacts to Forest Lake during the summer months has been the increase in water temperature due to the heat. Runoff from the rainfall also carries additional nutrients into the lake.

This weather combined with the runoff provides ideal conditions for both green and blue-green algae to grow. Council is aware of the recent changes at the lake which includes an increase in green algae growth in some areas, a general decrease in clarity and some musty odours at the lake.

As a result, Council has been extracting small pockets of algal build-up in the pockets near Freshwater Circuit and Santorini Place. Following storm events in December and January, Council has removed storm debris from lake inlets and stormwater quality improvement device units.

Council anticipated the changes prior to the recent weather events and has been regularly monitoring the behaviour of the lake. Council will continue to monitor the lake with the assistance of the Forest Lake expert working group.

If any more blue-green algal blooms occur at the lake in accessible areas, it will be removed by suction trucks.

Salvinia growth

You may have noticed Salvinia has continued to grow at Forest Lake. The Salvinia growth is helping the lake by reducing the nutrient levels in the water, which minimises the risk of blue-green algal blooms at the lake.

Council has been regularly monitoring the growth with the assistance of the working group. Parts of the Salvinia growth will be harvested. There was a trial harvest at the lake with a small machine in early March 2020. During the trial, it was decided a larger machine would be more effective for this work. It is anticipated the works will resume with the larger equipment in coming weeks, weather and site conditions permitting. The harvest will be carefully managed to ensure that over half of the Salvinia growth remains in the lake so that it continues to reduce nutrient levels.

Maintenance works

Council has recently been undertaking drainage maintenance works along the table drain that leads into Forest Lake at Seabrook Crescent, Forest Lake. The works extend from Jindabyne Circuit to Illawarra Close and form part of Council's drainage and creek rehabilitation maintenance program.

The works include:

  • removal of undesirable tree species
  • desilting of existing sediment ponds
  • clearing of existing drainage infrastructure
  • channel reinstatement
  • bank stabilisation
  • installation of grade and floor stabilisation structures to reduce erosion and bed scour.

These works are ongoing and are expected to be completed by the end of June 2020.

Council will also continue to do routine inspections and maintenance at the lake throughout summer. During these visits, the team will

  • test the lake water
  • treat weeds around the lake
  • collect litter
  • clear traps
  • monitor and manage any changes to the lake environment.

Ibis management plan update

Council has been working hard to address the growing ibis population on the small islands and in vegetation at the lake. This has contributed to the excess nutrients in the lake.

As part of Council's ibis management plan, wildlife consultants have been managing the ibis population through egg and nest movement.

Council undertook an additional vegetation management plan for the lake. As part of this plan, Council removed and treated some vegetation to deter ibis from the lake. These reeds and rushes will be replaced with plants that are less suitable for ibis roosting this year. Planting will be determined by the cattle egret bird breeding season which is from September to March.

The wildlife consultants have continued to monitor the number of ibis at the lake to determine if the management plan has been successful to date. The number of ibis observed roosting at Forest Lake in February 2020 was 42 birds. This is a significant decrease from the highest counts of ibis at approximately 460 in January 2018 and 440 in July 2018.

This data demonstrates that the ibis management plan has been effective in reducing the number of ibis at Forest Lake. Overall, this should benefit the lake health, as fewer ibis means a decrease in the unwanted nutrients that they bring to the lake through their droppings.

Project works

Council developed the Forest Lake Strategic Management Plan in 2019. This outlines the best evidence-based solutions which have been recommended by the expert working group to improve the long term health of Forest Lake.

The plan recommends two stages of lake works. The first stage will involve strategic desilting at the two inlet areas of the lake, to reduce nutrient loads where the sediment deposition and nutrient levels are highest. The purpose of this stage is to rectify the nutrient levels in the lake which are contributing to the algal blooms.

The second stage of the project works will involve replanting in the desilted areas and more broadly across the lake. The replanting program is a major exercise and plans to introduce around 70,000 new plants to help reduce the nutrient levels in the lake. The project is at the very early stages of the planting process - sourcing seeds and soil and starting to grow some of the 70,000 plants for the lake. Some of the plants have a different life cycle. This is being carefully managed and timed to ensure the seeds are planted at the right time.

The methodology and exact timeframes for the desilting and replanting activities require further investigation and are subject to permits and weather and site conditions.

Expert working group

The issues affecting the health of Forest Lake are complex and required the attention of dedicated experts. In April 2019, Council developed a working group made up of Council scientists and external water experts to ensure that any future works undertaken are based on the best expert advice.

Supporting Council's experts are Professor David Hamilton, Deputy Director of the Australian Rivers Institute at Griffith University and Tony Webster, one of Australia's leading practitioners in the catchment modelling and water quality field.

Strategic management plan

The Forest Lake Strategic Management Plan has been developed by the expert working group and outlines the best evidence-based solutions to improve the long-term health of Forest Lake.

The purpose of the strategic management plan is to:

  • document the current condition and existing maintenance practices at the lake
  • document outcomes from the Forest Lake working group, which was established in April 2019 to bring Council and external experts together to develop a robust plan for the lake's health
  • identify future lake management options to reduce the frequency and abundance of algal blooms, while also improving the overall condition of the lake
  • recommend a lake monitoring plan to address data gaps and ensure the long-term health of the lake.

Download the strategic plan in your preferred format:

Proposed solution

Council is committed to building and maintaining the infrastructure for the future while protecting our unique lifestyle, local greenspace and parks. To find the best solution for the lake, the expert working group divided lake management options into four categories:

  • reducing nutrient levels (both those entering the lake and those already in the lake)
  • managing light availability
  • recreating a more 'plant-based' lake system
  • potentially increasing water movement in the lake.

Additional monitoring is proposed to address key data gaps over time and continue to adapt the management of the lake.

Timing

The plan recommends strategic desilting in areas of the lake, followed by planting in those zones and more broadly across the open water areas of the lake.

The methodology and exact timeframes for the desilting and replanting activities require further investigation and are subject to permit, weather and site conditions. Once these details are finalised, Council will provide advance notification of the works.  

This table includes the timing for desilting and replanting activities for Forest Lake.
Action Date
Final strategic management plan Complete July 2019
Planning and design Complete August 2019
Approvals, permits, procurement and tendering August 2019-March 2020
Desilting and replanting  April 2020-late 2020 

Findings from earlier investigation works

Council undertook investigations on the lake via boats and sampling equipment in March 2019.  By sampling at different depths throughout the water column, these important investigations provided a more in-depth understanding of water quality. The following sampling was undertaken as part of the strategic management plan.

Water quality sampling and analysis (surface water, groundwater and sediment)

  • physicochemical parameters (pH, dissolved oxygen, conductivity, temperature, turbidity
  • blue-green algae (species, toxicity)
  • total dissolved solids
  • total suspended solids
  • total alkalinity
  • total organic carbon
  • bicarbonate
  • carbonate
  • hydroxide
  • chloride
  • major ions (calcium, magnesium, sodium, potassium)
  • nutrients (ammonium, oxides of nitrogen (nitrite, nitrate), nitrite, nitrate, total Kieldahl nitrogen, total nitrogen, ortho-phosphorus, total phosphorus)'
  • water hardness
  • total and dissolved metals and metalloids (aluminium, arsenic, boran, barium, cadmium, cobalt, chromium, copper, iron, manganese, molybdenum, nickel, lead, zinc, mercury
  • silica
  • sulphur
  • polycyclic aromatic hydrocarbons
  • polycholorinated biphenyls
  • total petroleum hydrocarbons
  • BTEX
  • organochlorine and organophosphorus pesticides.

Aquatic ecological assessment

  • aquatic vegetation
  • macroinvertebrate communities
  • fish communities
  • turtle communities
  • birds.

The key findings from the investigation works are listed below.

  • Forest Lake supports an array of biodiversity including six native fish species, over 50 bird species, a high diversity of aquatic macroinvertebrates and three native submerged aquatic plants.
  • Despite observed algal and salvinia blooms, the presence of aquatic macroinvertebrates and native submerged aquatic plants indicate better water quality than expected. These species are usually quite sensitive to changes in water quality and poor light penetration.
  • The six native fish species identified include eel-tailed catfish, spangled perch, garfish and eels, and occured in healthy numbers.
  • Although only a few turtles were sampled formally as part of the investigations, a large number of short-necked turtles were observed and believed to be in good health.

The work helped Council better understand the current conditions and species at the lake, which informed the development of the strategic management plan.

If you would like a copy of the sampling report, email the project team.

Griffith University project

A Griffith University student research project was completed in partnership with Council to model water quality and ecosystem dynamics at Forest Lake. This project was coordinated through the Australian Rivers Institute at Griffith University, as part of ongoing research projects being undertaken with Council.

The modelling provided an understanding of the present state of the lake’s ecology and water quality, based on available data. A permanent water quality logging station has also been installed to help build-on available data for this modelling over time. With new data, this modelling can be re-run in future to better predict causes of algal blooms in the lake and continue to improve lake management.

The research project was concluded in late May 2019 and the findings were provided to the project team developing the Forest Lake Strategic Management Plan.   

Get involved

Council has received some interest from the community to form a new Habitat Brisbane group in Forest Lake. The Habitat Brisbane Program provides an opportunity for the local community to work with Council to protect and enhance the habitat values of local parks and natural areas.

A number of sites including Desoto Park and Hancock Park-Pine Village Park have been suggested by local residents as potential Habitat Brisbane sites. Although not directly located on the lake, Desoto Park has bushland registered as Endangered Regional Ecosystems and is a strategic corridor linking Greenbank and Oxley Creek, with run-off into Forest Lake.

If you’re passionate about the environment and are keen to make a difference with hands-on volunteering or would like to learn more, phone Council on 07 3403 8888 or email the project team.

Register for updates

Register for updates on the Forest Lake management plan.

More information

For more information:

  • email the project team
  • phone the project team on 1800 669 416 (during business hours)
  • phone Council's Contact Centre on 07 3403 8888 (after hours).
Last updated:11 March 2020