2018-2024: Ross River Dam (Queensland)
“RRD harbours two types of harmful algae blooms (HABs): Cyanobacteria (also known as blue green algae) and Diatoms. Cyanobacteria were first detected in RRD in 2018. Since then, a significant bloom has developed and treatment has required ongoing management. Since the onset of cyanobacteria blooms within RRD, significant improvements have been made to the water treatment process at Douglas WTP including: an improved monitoring program, pre-chlorination on all filters, PAC dosing on Modules 1 and 2 and the addition of clarification on modules 3 and 4. Additionally, the design for a permanent, more effective PAC dosing system covering all modules is in progress since completion of the raw water pipeline replacement. Finally, filter media replacement in modules 3 and 4 are under investigation with the aim to improve filtered water quality.
Every summer the bloom duration and biovolume increases. The average
cyanobacteria biovolume in 2023/2024 FY (7.23 mm3/L) increased by 44%
from the previous FY (5.02 mm3/L). The weather conditions of long hot days
and wash-in of nutrients from rainfall provide optimal conditions for growth.
The dominant species is Raphidiopsis raciborskii which produces a toxin called Cylindrospermopsin. This toxin is mitigated through the treatment process and has not been detected in the treated water.
Diatoms were first detected in significant concentrations within RRD in 2021.
Since this detection, several significant blooms have occurred, the worst of which occurred between September 2023 and November 2023. Due to their size, this bloom reduced the effective capacity of Douglas WTP to supply treated water. TCC continues to work with Trility, the Office of Water Supply Regulation, Queensland Health and industry experts to address the risks associated with HAB’s and assess and implement management and treatment strategies at a catchment, dam and treatment level. Despite continued implementation of these strategies and measures, risks associated with HAB’s remain a concern. A part of managing these risks includes the implementation of water conservation and restriction measures, particularly during high demand periods and significant HAB’s to ensure that clean, safe and high quality drinking water is consistently provided to the Townsville community.”
Townsville Council Drinking Water Quality Management Plan 2023/2024