Mannus Lake UTS Study
In December 2018 Council engaged the University of Technology Sydney (UTS), to undertake a research study of the algae bloom in Mannus Lake to better understand the causes of toxic cyanobacterial blooms at Mannus Lake and to indicate possible management approaches.
Mannus Lake has experienced severe algal blooms of the potentially toxic cyanobacteria Chrysosporum ovalisporum. The bloom was first noticed between late 2017 and early 2018 after public concerns about downstream water quality.
The study aimed to:
- Monitor lake for blooms for public health safety and reporting
- Determine the causes of the algal blooms in the lake;
- Determine management strategies to stop or reduce future algal blooms, costs to implement and run, and determine likely benefits.
After the study period several factors were identified that were likely contributing to the formation of the bloom. Thermal stratification of the water column was found to be a key factor in stimulating the bloom, and a possible management approach was suggested to artificially mix the water column with a propeller, air curtain or pump.
In December 2019, a mixer was installed at Mannus Lake and UTS was again engaged to monitor the bloom dynamics and evaluate the effectiveness of the mixer.
UTS Mannus Lake Study Reports
Report September 2022
This report covers the 2021 calendar year through to August 2022 and information is presented within the context of the previous years.
In the summers of 2020-21 and 2021-22 no red alert level algal blooms occurred.
The influence of the mixer on this reduction remains unclear as these years were also wet with considerable inflow events to the lake influencing mixing events and lake flushing.
Inflows were also much higher in magnitude and more frequent in the summers of 2020-21 and especially 2021-22 compared to previous years due to above average rainfall resulting from La Nina weather patterns.
With 3 more years of monitoring planned it should become clear as to whether the mixer is working, as a summer with few inflows is required to better understand the performance of the mixer at reducing algal blooms.
Click the link below to access the UTS September 2022 Report
Mannus Lake Cyanobacteria Study Sept 2022(PDF, 2MB)
Report July 2021
This report covers the 2020 calendar year and information is presented within the context of the previous years.
In December 2019, a mixer was installed in Mannus Lake, however, a cyanobacterial bloom had already formed. Unfortunately, early observations of the mixer indicated that thermal stratification was still forming.
In the summer of 2020, as the mixer had not shown desired performance, the position of the mixer was adjusted based on the bathymetry of the lake.
At the time of mixer re-positioning, there was low cyanobacterial biomass in the lake, and a red-alert bloom had not formed.
This UTS report addresses the state of Mannus Lake through 2020 and also within the context of previous years. The effectiveness of the mixer in reducing thermal stratification is discussed.
Click the link below to read the UTS Mannus Lake Cyanobacteria Study - Stage 2 Report
Report-July-2021-Mannus-Lake-Cyanobacteria-Study.pdf(PDF, 2MB)
Interim Report – June 2019
The interim report from UTS will be tabled at the July 2019 Ordinary Council meeting. It is expected that Council will be able to utilise the interim report to initiate a solution in advance of summer 2019/20.
The interim report examines the data collected to date from UTS sampling between December 2018 and early May 2019 and gives preliminary conclusions.
Sampling started just after the formation of another Chrysosporum bloom in November/December 2018 and analysis includes the algal count data that council had collected prior to this and other data collected by council.
Click here to read the Mannus Lake blue-green algal bloom management study – Interim Report(PDF, 1MB)
Please contact Council on 1300 ASK SVC (1300 275 782) or email [email protected] with any questions.