Can Lake Burley Griffin's blue-green algae problem be fixed with ultrasound? Um, not really

The National Capital Authority (NCA) is heading back to the drawing board after a novel idea to rid Lake Burley Griffin of its blue-green algae problem using ultrasound appears to have failed.

Blue-green algae is another name for cyanobacteria, which reproduces quickly and forms ‘blooms’ in still or slow-moving water with abundant sunlight and sufficient levels of nutrients, especially nitrogen and phosphorus.

In humans, blue-green algae can cause anything from skin rashes to nerve and organ damage, depending on the level of exposure.

Every year, between the warmer months of October and April, the NCA monitors the lake’s water quality and closes certain sites to recreational activities when the levels get too high.

It also “works proactively with other land managers in the lake’s catchment area and supports work to improve the quality of the water flowing into the lake”, according to the NCA’s 2023-24 Annual Report.

But ultimately, they’d love to find a permanent fix.

Over the past two seasons, the NCA has trialled the use of “ultrasonic pontoons” to control the growth of blue-green algae. The theory goes that by creating vibrations in the water column, the algae cells can be destroyed, and the blooms effectively vanish.

Two pontoons were installed in popular swimming spots on the lake in December 2022 at Lotus Bay and West Basin.

Between then and June 2024, the NCA went about business as usual and collected water samples at all the recreational sites during the warmer months, and there was good news.

According to the annual report, “there was a decrease of around 40 per cent in the levels of blue-green algae at both test sites compared with the previous recreation seasons”.

“However, all other recreation sites around the lake showed a similar reduction in blue-green algae levels over the same period,” it went on.

“These results suggest that reduction in total BGA is likely due to environmental factors, than directly attributable to the introduction of ultrasonic pontoons.”

The test sites were also closed just as often over the seasons as the other sites.

“Given the results, it is difficult to definitively state that introduction of the ultrasonic pontoons at the test sites had a positive impact on water quality at those locations,” the NCA wrote.

“The NCA will continue to monitor water quality at both sites to determine whether water quality worsens following the removal of the pontoons.”

Undefeated, an NCA spokesperson told Region that while “this blue-green algae trial did not deliver the results we had hoped for”, the authority “will continue to consider innovative, low-cost interventions into the future”.

“Lake Burley Griffin is one of the most iconic parts of the national capital, and improving its water quality is something that the community has long called for, which is why the NCA undertook this trial,” the spokesperson said.

“The key driver for blue-green algae in Lake Burley Griffin is the amount of nutrients and quality of water flowing into the lake, which is why the NCA is working with catchment managers, including the ACT and NSW governments, to improve water quality.”

On a more local level, the ACT Government has commissioned the University of Canberra (UC) to look at the internal cycling of nutrients within the lake, starting last year and running over at least two summers.

“We’re understanding some of the physical characteristics of the lake, what the flow is and where the waters separate to form different layers in the lake,” UC’s Dr Rodney Ubrihien said.

This will underpin the development of a ‘Healthy Waterways Plan’ for Lake Burley Griffin, according to the government’s Environment, Planning and Sustainable Development Directorate, which will be released for public comment in 2025.