A flow of fresh water has been released into the River Torrens this morning to control blue-green algae levels in the CBD’s Torrens Lake, following the start of Green Adelaide’s annual summer blue-green algae monitoring project last week.

Fresh water flowing down the River Torrens at Gorge Weir in the Adelaide Hills.

Recent monitoring in the CBD’s Torrens Lake showed a rapid increase in blue-green algae concentrations in the lake, and combined with Adelaide’s upcoming warm temperatures and low rainfall, it was assessed that blue-green algae levels could reach bloom levels soon.

As a preventative measure, a flow of fresh water has been released this morning from Kangaroo Creek Reservoir to freshen the lake’s water quality and reduce blue-green algae levels in the water.

3-day fresh water flow event to improve water quality

Green Adelaide ecologist Dr Nadine Kelly said that the fresh water flow was released as a preventative measure to stop a potential toxic blue-green algae outbreak in the Torrens Lake.

“These fresh water flow events are a standard measure during the summer for the Torrens Lake to maintain its water quality, and to keep it open for recreational use for the public to enjoy," Dr Kelly said.

“At high concentrations, toxins from some blue-green algae species can be harmful to people and wildlife.”

This morning a flow of water from Kangaroo Creek Reservoir was released and the fresh water will flow through the system for the next 3-days. It is expected that the fresh flow of water will reach Torrens Lake tomorrow (Tuesday, 21 Dec) and flow out to the sea at Henley Beach South from Wednesday (22 Dec) until Christmas Day. A channel has already been excavated on the beach as part of the project to direct river water straight out to sea.

Dr Kelly said that over the next 3-days the flow will help reduce water temperature and dilute nutrient levels that promote blue-green algae growth in the Torrens Lake.

“People may notice a higher than usual river flow along the Torrens as the fresh water makes its way from the hills, through the city, and to the Torrens Outlet at Henley Beach South," she said.

“The water flowing out to sea is not stormwater, but as with all flows into the sea from urban areas, beach goers are encouraged to avoid swimming in turbid or discoloured waters.”

This year is the eleventh year of the River Torrens Water Quality Improvement Project, which has been successful in preventing Torrens Lake blue-green algae outbreaks and lake closures for the past 8 years. The last fresh flow preventative event was in 2019.

Blue-green algae is different from the usual duckweed algae seen along the Torrens. Both are natural parts of the river system, however duckweed is safe and blue-green algae can be toxic to people and wildlife in large doses.

The project is a collaboration between Green Adelaide, Department for Environment and Water, SA Water, Environment Protection Authority and City of Adelaide.

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