The iconic Torrens Lake is an important community asset and central destination for Adelaide visitors and locals alike.
Situated in the heart of the city, the lake is the section of the River Torrens between Frome Road and the River Torrens weir.
Unfortunately though, it can get sick with blue-green algae (cyanobacteria) blooms, turning the usually postcard-worthy landscape into an eyesore.
But what exactly is blue-green algae, why does it form and how do we get rid of it?
What is blue-green algae?
Blue-green algae is a naturally occurring microscopic bacteria that grows in warm, still and nutrient-rich water.
Every summer in Adelaide when Torrens Lake becomes warm, the risk of blue-green algae emerges.
How it works is that when it rains, rainwater collects nutrients as it runs off hard surfaces in the urban environment, such as roads, footpaths and buildings.
Eventually this water ends up in waterways and catchments, like Torrens Lake.
This nutrient-rich water sits still in the lake and warms up under the hot summer sun, making it a prime breeding ground for blue-green algae.
Why is blue-green algae bad?
As blue-green algae blooms increase in the lake, it begins to take over altogether – outcompeting other species and discolouring the water to form scums and produce a nasty smell.
It also releases toxins that can be harmful to you or your pet if you come into contact with it – you might get a rash or a stomach ache.
Once the algae reaches these levels, Torrens Lake is closed for recreational use. This closure can last for weeks, or even months.
What is being done to prevent blue-green algae?
It’s not all doom and gloom though. A team of experts have been working on the River Torrens Water Quality Improvement Project to closely monitor and control blue-green algae outbreaks – and therefore preventing lake closures – for the past seven years.
Every summer, Green Adelaide’s River Torrens Water Quality Improvement Project team closely monitor algal levels in the lake.
So far this season, occasional but heavy rains have kept algae levels low so the project team hasn’t needed to intervene.
The rain helps by diluting the water, mixing it up and cooling it down, creating less favourable conditions for the blue-green algae, and therefore disrupting its growth.
But what happens if it doesn’t rain for a while?
The best treatment method is to release a fresh flow of water from upstream at Kangaroo Creek in the Adelaide Hills.
It has the same effect as a heavy rainfall event, and brings the lake’s algal numbers back to an acceptable level.
The project team that cares for Torrens Lake is comprised of members from Green Adelaide, the City of Adelaide, SA Water and the Environmental Protection Authority. For more information about the project, visitGreen Adelaide's website.