BCC Continues to Implement Long-term Solutions to Improve Water Quality in Forest Lake

Brisbane City Council is currently in the midst of a $1.1 million investment into the implementation of long-term solutions to address the issues and improve the health of Forest Lake, as part of an overall Forest Lake management plan.

Stage One : Desilting & Reducing the Nutrient Load

The Forest Lake Management Plan provides an evidence-based solution in two stages. Stage One involves strategic desilting at both of the lake’s inlet areas of the lake, aiming to reduce nutrient loads where the nutrient and sediment levels are highest. This will ensure control and management of algal blooms across the lake.

Algal Blooms

Over the summer months, both heat and rainfall have contributed to some significant changes in Forest Lake.

Council has cleaned up debris from lake inlets and from various stormwater quality improvement device units, after storm events in late 2019 and early 2020. Rainfall has resulted in a runoff, introducing additional nutrients into the lake.

Increased water temperature due to the summer weather, coupled with the runoff, constitute ideal conditions for the growth of blue-green and green algae, leading to an observable decrease in water clarity in the lake, and the musty odour that residents and visitors have characteristically observed.

As a result, Council has been extracting pockets of algal build-up in the pockets near Santorini Place and Freshwater Circuit. Likewise, suction trucks are on standby to remove algal blooms as they occur in accessible areas of the lake.

Photo Credit: Enya2008/Wikimedia Commons

Harvesting Salvinia growth

Salvinia, an invasive plant, has continued to grow at Forest Lake. This growth has actually been helping to minimise blue-green algal blooms at the lake by reducing the nutrient levels in the water.

To prevent Salvinia, overgrowth, Council has been conducting regular monitoring and harvesting. A trial harvest was done in March 2020, using a small machine which was deemed inadequate. Larger equipment has been allocated and harvesting has been planned to ensure that over half of the current Salvinia growth remains in the lake, to make sure that nutrients are kept at a level that does not encourage algal growth.

Drainage Maintenance

As part of Council’s drainage and creek rehabilitation maintenance program, drainage maintenance works have been performed from Jindabyne Circuit to Illawarra Close, along the table drain that leads into Forest Lake at Seabrook Crescent, Forest Lake.

Ongoing maintenance works include desilting of existing sediment ponds, removal of undesirable tree species, clearing of existing drainage infrastructure, channel reinstatement, and stabilisation of the lake’s banks to reduce bed scour and erosion. Maintenance are expected to be completed by mid-2020.

Routine inspection and maintenance procedures are in place to ensure collection of litter, clearing of traps, treatment of weeds, testing of the lake water and monitoring the overall health of the lake.

Management of the Ibis Population

Ibises in Bird Island a.k.a. “Bin Chicken Island” on Forest Lake

In February 2020, 42 ibises were observed to be roosting at Forest Lake. Waste droppings from the ibis population on the lake has led to excess nutrients which also contributed to algal bloom in the past. The 2020 population is already a significant decline from over 400 ibises observed in 2018.

Wildlife consultants have recommended egg and nest movement, along with vegetation management to further manage the ibis population and prevent it from increasing again.

Vegetation management will ensure that reeds and rushes where ibises roost will be replaced with something less suitable for them to inhabit. Council has announced that the planting of alternate vegetation will be determined by the cattle egret bird breeding season, from September to March.

Stage Two : Replanting Program

Stage Two involves introducing 70,000 new plants in the desilted areas of the lake and also, more broadly around it to further reduce the nutrient levels in the lake. Activities for the first half of 2020 include sourcing of seeds and soil, plus beginning to grow the plants for the lake, according to their life cycles.

Overall Solution

Overall, the Forest Lake Expert Working Group has divided its lake management options into four categories:

  • reducing nutrient levels by controlling contributing factors entering the lake and within it;
  • managing light availability;
  • recreating a more ‘plant-based’ lake system; and
  • potentially increasing water movement in the lake to reduce stagnation.


BCC has announced a general methodology and schedule which will be updated over time. Below is a copy from the BCC site.

Final strategic management planComplete July 2019
Planning and designComplete August 2019
Approvals, permits, procurement and tenderingAugust 2019-March 2020
Desilting and replanting April 2020-late 2020

BCC Releases Forest Lake Management Plan, Range of Measures to Keep Lake Healthy Revealed

Council will invest in a long-term plan that will cost more than $1 million over  two-and-a-half years, along with a range of other measures, as part of the Forest Lake management plan to address the ongoing issues affecting the lake.

A man-made wetland, Forest Lake was designed to improve water quality flowing into the Oxley Creek and provide recreational and visual amenity for the community. Over the last few years, however, the lake was beset with a number of environmental issues including blue-green algae growth; water weed salvinia growth; and the increasing population of ibis on Bird Island and other areas around the lake.

Developed by the Council’s expert working group, the Forest Lake Strategic Management Plan outlines the best evidence-based solutions for the lake. The lake management options are divided into four categories:

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

 Forest Lake
Photo credit: Brisbane City Council / flickr

Council will invest more than $1 million, spread over two-and-a-half years, to implement  the long-term program along with a range of other measures to improve the health of Forest Lake

The two-and-a-half-year program will implement measures to reduce the lake’s sediment and nutrient levels, as well as enhance the water movement: 

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

Desilting and replanting activities is planned to be undertaken in April 2020 to late 2020.These activities will be undertaken along with ibis management program; salvinia weed harvesting; cleaning out litter traps  upstream of the lake; and algae scum collection and disposal.

You can also do your part in keeping the Forest Lake healthy

  • Don’t feed the ducks or other animals – Uneaten food settles at the bottom of the lake, causing sediment build-up and algal blooms that impact the lake’s health.
  • Pick up after your dog – Over time, nutrients from droppings that were washed into the waterways cause build-up of algal blooms.
  • Stop other nutrients flowing into nearby waterways –  Examples: Wash your car on the lawn, reduce fertiliser use, particularly before rain; and collect lawn clippings after mowing.