Cox Bay lake clay trials continue

Trial work exploring clay-based products to reduce phosphorus concentrations and algal growth has been continuing in Mandurah’s Cox Bay North Lake this summer.

We applied a phosphorus-binding clay product called hydrotalcite clay (HT-clay) to the lake in early November 2024. A few hours after the application, the phosphate concentrations in the lake had reduced by about 95 per cent. Phosphate is a bioavailable form of phosphorus that is immediately available to fuel algal growth in waterways.

Environmental Officer Ryan Kam from the Department of Water and Environmental Regulation, said the application was also effective at removing algal growth.

“As you can see in the picture, one day after the treatment the water was much clearer. This means the clay was also effective in removing algae, by causing them to clump and sink to the bottom of the lake,” said Ryan.

Our next application of two clay products – HT-clay and Phoslock – took place in early December.

Before this second application, phosphate concentrations remained below detection limits; however, phosphorus was still present in the algae growing in the lake. This application was effective at reducing the algae in the lake by 84 per cent, and the associated total phosphorus by 74 per cent.

“Since the lake has ongoing sources of phosphorus, including from groundwater, we expect some algal growth to persist in the lake over summer. However, the water quality treatments are likely to have reduced the severity of algal blooms in the lake,” said Ryan.

“The trial is also giving us important insights into how these clay products work under different environmental conditions.”

Our thanks go to the City of Mandurah for their support with this trial, which is funded by Healthy Estuaries WA and Bindjareb Djilba (Peel-Harvey estuary) Protection Plan – State Government Initiatives to improve the health of the estuary.

More about the trial: https://estuaries.dwer.wa.gov.au/strategies/innovative-remediation/phosphorus-binding-clay-trials/