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 on 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 - late 2019 

Summer update  

The temperatures are rising in Brisbane as we approach the summer months. Brisbane, and South East Queensland, are also currently in the ‘drought response phase’ of Seqwater’s Drought Response Plan. This is due to the SEQ Water Grid drinking water supply capacity falling to below 60% in November 2019.

We understand that there may be some changes in the behaviour of the lake during this period and have provided some further information on what to expect. 

The lake water level is currently low, this is due to the drought that is currently affecting Brisbane, and South East Queensland. Also, one of the greatest impacts to Forest Lake during the summer months will be the increase in water temperature due to the summer heat. The storms we usually encounter during the summer period are also another potential impact. The run-off from these storms can carry additional nutrients into the lake. These two elements combined provide ideal conditions for both green and blue-green algae to grow.  

As a result of these elements, water quality of the lake may change during the coming months. You may notice a change in clarity, the intensity of the green colour could increase and it is possible that musty odours could be present at the lake. The occurrence and severity of these possible impacts is dependent on a number of environmental factors, including wind, rainfall and temperature.

You may have noticed salvinia is growing at Forest Lake. The current salvinia growth is helping the lake by reducing the nutrient levels in the water, this minimises the risk of blue-green algal blooms at the lake. Council are aware of the salvinia growing in the lake and are continuing to monitor the growth with the assistance of the working group. 

Council will continue to do routine inspections and maintenance at the lake during the summer months. During these visits the team will be

  • testing the lake water 
  • treating weeds around the lake
  • collecting litter
  • clearing out traps. 

If any blue-green algal blooms do occur at the lake and the scum is in accessible areas it will be removed by suction trucks.

If you do see any blue-green algal blooms at Forest Lake, please call 07 3403 8888. 

What you can do 

As a local resident living in the lake catchment, you can also play a part in reducing the build-up of nutrients and sediment entering the lake. Some of the things that we can all do in our day-to-day lives to help improve the health of the lake are: 

  • washing cars on the lawn 
  • reducing fertiliser use, particularly before rain 
  • collecting lawn clippings
  • not feeding the ducks and wader birds 
  • picking up dog droppings.

More information on how you can help save water is located the Drought Response page.

Water quality station

Council has recently installed a new permanent real-time water quality station at Forest Lake. This equipment monitors the algae concentrations, dissolved oxygen and other water quality attributes in the lake. As part of the water quality station, Council has installed two water quality loggers in the centre of the lake, one at the water surface and one near the bottom of the lake.

The new data collated from this water quality station will help inform Griffith University modelling to understand the lake before and after proposed works, to ensure that management actions are achieving the necessary outcomes. In the long-term, the data will also be used to predict future algal blooms and future remediation measures.

Ibis Management Plan update

Council has been working hard in 2019 to address the growing ibis population on the small islands and in vegetation at the lake which have 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 management.

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. The reeds and rushes which have been removed will be replaced in 2020 with plants that are less suitable for ibis roosting (replanting timing is determined by the ibis 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 this month was 105 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 indicated 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.

View a graph highlighting the ibis roost count at Forest Lake:

Forest Lake ibis roost counts

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 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 to start in April 2020, followed by planting in those zones and more broadly across the open water areas of the lake.

In order to deliver the best possible outcomes to improve the health of the lake, it is important that these critical works are undertaken at the optimum time of year when weather conditions are favourable for the desilting and replanting works. The timeline below for the desilting and replanting activities has been recommended by the working group, including experts Tony Weber and Professor David Hamilton.

The intent of this timing is to avoid the summer storm ‘wet season’ and, weather permitting, allow new plants time to establish before the next wet summer storm season and potential flood events. Timing of the work is subject to weather and site conditions.

The expert working group has advised that if the works were undertaken during the summer storm ‘wet season’, there is a high risk that desilting and planting could be impacted by rainfall and flooding, resulting in ineffective desilting efforts, damage to equipment and washing away or drowning of the new plants.

The methodology and exact timeframes for the desilting and replanting activities require further investigation. 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 

This new program of activities will be undertaken in addition to Council’s existing efforts to manage Forest Lake including:

  • an ibis management program
  • cleaning out litter traps upstream of the lake
  • algae scum collection and disposal.

Findings from earlier investigation works

From March 2019, Council undertook investigations on the lake via boats and sampling equipment.  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)

  • physico-chemical 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:16 December 2019