Key points
- Harmful blooms form when specific species and environmental conditions combine, often building gradually before becoming more visible.
- By combining field research, long-term collections and satellite data, scientists are improving our ability to detect risks earlier and respond more effectively.
- Not all algal blooms are harmful. Many are a natural and important part of healthy ecosystems.
Algal blooms can seem to appear overnight.
A stretch of ocean that looked clear days earlier can suddenly appear discoloured and sometimes pose risks to ecosystems and human health.
But scientists say blooms are rarely sudden – understanding what happens before they appear is key to managing them.
Across Australia, CSIRO researchers are working with partners to piece together that hidden story, building an early warning system for harmful algal blooms by combining field collections, environmental science and satellite technology.
This is part of a broader push through initiatives like CSIRO’s AquaWatch Australia program, which is progressing towards a fully operational, national water quality monitoring system.
Together, these approaches are helping scientists and communities better predict, understand and respond to changes in our coastal waters. So, what’s really going on beneath the surface?
A visible tipping point
CSIRO researcher Dr Jodie van de Kamp explained that algal blooms are often the result of gradual environmental changes rather than sudden events.
“Algal blooms can seem to appear suddenly because the water quickly changes colour or clarity. But the conditions that can lead to a bloom usually develop over time,” said Dr van de Kamp.
“Water temperature can increase slowly, while nutrients can accumulate from runoff, wastewater or natural processes, creating the right environment for algae to grow.”
Warm water, sunlight, calm conditions and nutrients all play a role in whether algae remain part of a healthy ecosystem or grow into something more problematic.
“When these conditions line up, algae can grow rapidly and form visible blooms. But not all algal blooms are harmful,” said Dr van de Kamp.
Long-term ocean observing programs, such as the Integrated Marine Observing System (IMOS), help scientists understand the factors leading up to bloom events.
Using long-term archived DNA samples, researchers identified that the harmful species K. cristata had been present – at very low levels – over the last decade in South Australian waters.
Combined with other observations, this allows scientists to reconstruct the environmental conditions preceding a bloom.
Although algal blooms occur naturally and are an essential part of healthy ocean ecosystems, a smaller number of species can become problematic – producing toxins, causing fish kills, blocking sunlight or smothering fish gills.
Distinguishing between these outcomes is key to the science.
Why the species matters
To most people, a bloom might just look like discoloured water. But for algae scientists like Dr Kirralee Baker, identifying exactly which species are present is critical.
“Knowing which species is blooming tells us whether it’s a natural ecosystem event or something that is a potential risk and needs a rapid response,” said Dr Baker.
Enter: algal collections.
“An algal collection is like a living library of algae. Each strain is a verified reference that helps us understand which species are present and how they behave.”
At CSIRO, the Australian National Algae Culture Collection (ANACC) holds living cultures of microalgae that have been carefully identified and studied.
But identifying species isn’t always straightforward. Under a microscope, some algae can look almost identical, even when their impacts are very different. Each strain can be DNA-sequenced, creating high-quality reference sequences that anchor species identities with confidence.
Environmental DNA (eDNA) collected from water samples can then be matched against these reference sequences, allowing scientists to confirm which species are present – even when cells are too similar to distinguish visually or before blooms become visible.
These collections underpin everything from monitoring programs to the development of detection tools.
“Without a trusted reference library, it’s extremely difficult to interpret what we see in environmental samples or satellite imagery," said Dr Baker.
The collections also reveal just how diverse algae can be.
“Two algae can look remarkably similar but have completely different characteristics. Many have a similar cell shape, size and behaviour, yet differ in their toxin production, nutrient use and bloom dynamics.”
That complexity has been highlighted in recent research into Karenia, a group of microscopic algae linked to harmful blooms in South Australian waters.
Unmasking a hidden behaviour
The Karenia genus belongs to a group of algae known as dinoflagellates, single-celled organisms that can behave in surprising ways.
Some are thought to be ‘mixotrophic’, meaning they’re able to act like both plants and animals.
“Many dinoflagellates are suspected to be mixotrophs – that is, cells that can photosynthesise like plants and feed like animals. This dual lifestyle makes them incredibly adaptable and potentially more harmful under certain conditions,” said Dr Baker.
This ability to switch energy sources helps explain why some blooms persist or behave unpredictably.
Seeing patterns across entire coastlines
While collections help identify what is in the water, this work is also being integrated into CSIRO’s AquaWatch program, where algal collections and genomics research are contributing to new monitoring tools.
Alongside this, another tool is helping researchers see where and how blooms are developing.
“Satellites are like cameras in space that regularly orbit the Earth, taking images of its surface, including lakes, rivers and oceans. These images capture subtle changes in water colour, which can reveal what’s happening in the water below," explained Ms Janet Anstee, head of AquaWatch Australia.
“When water appears very green, it is often due to the presence of algae,” she said.
By measuring pigments such as chlorophyll, satellites can estimate how much algae are present and track how this changes over time.
“Because satellites collect images regularly, scientists can see whether an algal bloom is growing or shrinking, and track how it is moving across a lake, river or coastal area.”
Satellite data offers capabilities that traditional water sampling cannot.
“Satellite observations complement these methods by providing insights that are otherwise difficult to achieve at scale. With a single image, satellites can observe entire lakes, river systems, coastal regions or even whole countries,” Ms Anstee explained.
Bringing the data together
“AquaWatch uses satellite observations to build a consistent, continental-wide picture of water health,” said Ms Anstee.
By integrating satellite imagery with on-the-ground sampling and environmental data, the system provides a more complete and reliable understanding of what’s happening in Australian waters.
“A strength of AquaWatch is its ability to integrate ground and water-based measurements with satellite images, to provide more accurate assessment,” she said.
“By working with our collaborators and colleagues at CSIRO, we have an opportunity to work with them to develop a truly integrated system to better understand water quality.”
Increased investment since the South Australian bloom in 2025 is helping strengthen AquaWatch’s ability to provide advanced warning. A combined approach is vital because satellites alone can’t tell the whole story.
“For example, satellites generally cannot determine the exact species of algae present. They also cannot directly measure toxin concentrations.”
That’s why field sampling, laboratory analysis and collections remain essential.
Together, these approaches allow scientists to answer important questions: what species are present, what conditions are driving growth, and whether a bloom poses a risk.
From reacting to predicting
The ultimate goal of this research is to move from reacting to blooms after they appear, to predicting and preparing for them in advance.
“By understanding the environmental conditions that lead to blooms, scientists can see early warning signs such as rising nutrient levels or warming waters before a bloom becomes visible,” said Dr van de Kamp.
Sensitive detection tools like eDNA, combined with long-term observations from systems like IMOS and broad-scale satellite monitoring, play a role in speeding up responses.
“Satellites can detect the formation of algal blooms before they reach critical areas such as drinking water intakes or popular recreational sites. This means monitoring efforts can be targeted, and decisions made more quickly,” said Ms Anstee.
A bigger picture of change
Taken together, these different strands of science – collections, environmental monitoring and satellite observation – are helping scientists build a much clearer, more complete picture of how algal blooms form, evolve and spread.
“Looking at historical satellite images with real-time images reveals trends in water quality, effects of climate change and highlights areas where there are recurring problems,” Ms Anstee said.
Dr van de Kamp added: “Climate change is making conditions more favourable for algae to grow more often and more intensely. Warmer water speeds up algae growth, while changes in rainfall can increase nutrient run-off.”
No single approach can address harmful algal blooms on its own.
Research shows these outcomes are shaped by a combination of environmental and biological factors that build over time – and that they can be better understood, monitored and anticipated through coordinated scientific approaches.