What is blue-green algae?
Blue-green algae are a naturally occurring microscopic bacteria that live in water, from a group known as cyanobacteria.
Similar to plants, they photosynthesize, which essentially means that they suck in carbon dioxide and convert it to oxygen, with the help of the sun. But when the sun goes down, they flip to sucking up oxygen and converting it to carbon dioxide at night.
Things get a little more complicated when the weather – and therefore water – warms up, As the warm, slow moving waters are rich in nutrients which the algae feeds on to survive. This leads to an increase in blue-green algae, which can deprive plants and animals from oxygen.
When the blue-green algae grow rapidly, they can discolour the water, form scums and produce an unpleasant odour – this is known as an ‘algal bloom’.
Why do we excavate the Torrens Outlet?
There are many reasons! If a managed flow from upstream is required the excavation at the channel will mean that the water is directed out to sea, reducing risk of water sitting on the beach. An excavation is done before it is decided whether a flow will occur because blue-green algae levels can change quickly. The excavation also means that in the event of high summer rainfall, water is directed out to sea.
What does blue-green algae look like?
When there’s a blue-green algae bloom, it essentially looks like you’ve poured some kind of green paint or sludge on the top of the river.
Because they’re microscopic, blue-green algae can only be seen when there’s a group. Unless you can get one under a microscope! Sometimes an agal bloom is confused with the natural and completely safe occurrence of duckweed.
How do you get rid of blue-green algae in Torrens Lake?
Prevention is the best option, which is why our Torrens Lake Blue-Green Algae Management Program has been in play.
Through monitoring algae levels, and using managed flows of fresh water, the likelihood of a blue-green algal bloom occurring in the lake can be reduced – a strategy which has been successful since 2013.
If monitoring reveals that levels of blue-green algae are high, water from upstream storage is used to freshen lake water quality and dilute and displace algae to keep it at an acceptable level.
As well as managing blue-green algae, these flows can have a positive impact on aquatic plants and animals which benefit from water at a usually dry time of year.
Will blue-green algae go away on its own?
Blue-green algae is naturally occurring in all types of water, at a level which is not problematic for people or animals. While it is always there, it is only an issue if a bloom occurs.
If I see something green on the water is it blue-green algae?
Not always.
Duckweed, a floating plant that causes no harm to people, animals or the river system, is sometimes mistaken by the public as an algal bloom.
Duckweed is a good source of food for animals, particularly ducks – who would have guessed it?!
It also removes nutrients from the water that would otherwise be available for algae to feed on.
Can I help reduce nutrients entering waterways?
There are 3 ways you can reduce the nutrients, which the algae feeds on, going into our waterways. They are:
How harmful is blue-green algae?
Blue-green algae can take away oxygen from plants and animals in the water, when there’s a lot of it around it’s bad news for anything else living in the same area. At very high levels an algal bloom can occur which can result in toxins that are harmful for people and wildlife.
Algal blooms can last for several weeks or even months, and the toxins can hang around in the water for up to 3 months.
When blue-green algae blooms have occurred in the past, the Torrens Lake has had to be closed for public safety.
Thankfully the Torrens Lake Blue-Green Algae Management Program has prevented algal blooms since 2013.
How long does the excavation take?
The excavation can take 3-5 days depending on the extent of works to be done.
What is the difference between duckweed and blue-green algae?
Blue-green algae and duckweed do look similar but they are different in many ways! In short, duckweed is a naturally occurring tiny aquatic plant that is not harmful to people. In fact, it has a number of environmental benefits for the local ecosystem and wildlife.
Similar to blue-green algae, duckweed grows incredibly quickly in still water when it’s warm and sunny.
Duckweed can actually improve water quality as it reduces the potential for blue-green algae blooms by taking up the nutrients that the algae need to grow. Blue-green algae is potentially harmful to the environment and people and is something that needs to be managed. Duckweed does not need to be managed unless in the rare instances that it becomes carpeted across the lake and may result in boats propellors being caught on it.