What are Blue-green algae?
Algal bloom near Forbes NSW.
Photo: Arthur Mostead
“Blue-green algae” are not actually algae at all, they are a type of bacteria known as Cyanobacteria. They have some characteristics in common with algae – they photosynthesise, using light to produce oxygen and they need sunlight to grow. The two most common types in the River Murray are Anabaena and Microcystis . Blue-green algae are a natural part of the freshwater environment. If conditions are favourable, they reproduce at very high rates to form “blooms” – explosions in growth that dominate the aquatic environment, forming unpleasant and sometimes toxic scums.
What problems do Blue-green algae cause?
When blooms of blue-green algae occur, they interfere with other uses of the water and can affect human health and have far-reaching consequences for the environment and the economy. They affect water quality by causing undesirable tastes and odours, discolouration and unsightly scums. Blue-green algae can be toxic, with some species producing toxins that cause liver damage, stomach upsets and disorders of the nervous system in humans. Contact with high concentrations of blue-green algae can cause skin and eye irritations. Although no human deaths have been attributed to blue-green algal toxins, stock deaths have been documented and there is evidence of poisoning of wildlife and domestic pets.
As the bloom subsides, the dead and decaying algae can reduce the oxygen levels in the water, causing stress or death to other aquatic organisms such as fish. During periods of drought, aquatic ecosystems can be severely degraded by algal blooms.
Water supplies can be disrupted when filters and equipment are blocked and additional treatment (using activated carbon) is required to remove any dissolved toxins that are produced by some blue-green algae.
Blooms of blue-green algae can also prevent water-based leisure activities such as fishing and swimming, adversely affecting recreation and tourism.
What is being done about algal blooms?
Each State has extensive monitoring arrangements to detect and measure algae, and comprehensive emergency plans for dealing with algal blooms. They also have detailed arrangements for alerting the public of health risks, and the water supply authorities have advanced treatment techniques to remove dissolved toxins. The management of individual algal blooms is best undertaken at a local level, as the most effective approaches differ according to each bloom and each location. Along the River Murray there are Regional Algal Coordinating Committees (RACC's) covering the Albury to Tooleybuc area (the “Murray” RACC) and the Tooleybuc to the South Australian border area (the “Sunraysia” RACC). The RACC's include all the relevant managing authorities in both New South Wales and Victoria, and keep South Australia informed as well. Within South Australia, the management of algal blooms along the River Murray is similarly coordinated between the supply, management and health authorities.
Once a blue-green algal bloom occurs, very little can be done to stop it. Frequent testing of toxicity will help inform water use decisions and identify if alternative water supplies are required for stock and domestic uses. Drinking water supplies undergo additional treatment, using activated carbon to remove dissolved toxins and make the water safe for consumption.
Flushing the waterbody with higher flows can disperse blooms and break up stratification; however during drought the option of flushing is not always available.
Public alerts are issued to ensure all water users are aware of the problem and avoid direct contact with the water. These alerts are in the form of media statements and direct notifications to user groups.
What is the Authority doing about the algae problem?
When supplying the shares of water to the States, the Authority assists in the management of algae by varying flows where possible and managing additional flows when available, to reduce the likelihood and intensity of algal blooms in the River Murray. The required volumes of water can sometimes be supplied at a variable rate, “pulsing” the water and helping retard the development of stratification, which is a precursor to significant algal blooms. Partial drawdowns of weirpools can also help reduce stratification. Additional flows such as environmental water allocations of sufficient size to disperse algal blooms are not always available during drought.
In 1994 the Murray-Darling Basin Ministerial Council adopted an Algal Management Strategy as a framework for the algal management efforts of each State. The Algal Management Strategy emphasises nutrient reduction to address the underlying cause of algal growth, as well as scientific research to inform the management of algal blooms. A number of crucial research projects were undertaken by the former Murray-Darling Basin Commission, trialling methods for controlling blue-green algal blooms through river operations. The Commission also participated in research partnerships such as the National River Health Program, the National Eutrophication Management Program and the National River Contaminants Program, the findings of which have greatly improved the scientific understanding of algal growth and algal management. The scientific knowledge generated by these programs has been extensively applied by all States through their algal management programs.
Why do blue-green algae “bloom”?
A series of favourable environmental factors need to develop before blue-green algae will bloom. Those factors interact with each other in a complex way and it is therefore not possible to blame algal blooms on any single one of them. The factors which interact to favour the extensive growth of blue-green algae include:
Stable water columns – for blue-green algae to bloom the waterbody needs to have little or no flow, calm weather with little or no wind and hot sunny days. These factors allow the water column to stratify, which is where a layer of warm surface remains unmixed with the cooler, deeper water below it. Stratification can also result from differing densities through the water column, where saltier, denser water at the bottom remains unmixed with the fresher surface water above.
Sunlight – the water body needs to receive plenty of sunlight, with clear sunny days and low turbidity to allow the light to penetrate into the water.
Nutrients – there needs to be sufficient levels of nitrogen and phosphorus, in a form that is available to the algae. Phosphorus is usually present in sufficient quantities in the sediment of water bodies and can become available to algae when oxygen levels fall as a result of stratification, causing phosphorus to be released from the sediment by microbial activity. Nitrogen is a more mobile element than phosphorus and tends to be more generally available to algae. Microcystis growth can be limited by low nitrogen levels or particularly by a low nitrogen to phosphorus ratio. Anabaena are not limited by nitrogen levels as they can convert elemental nitrogen into biologically usable compounds of nitrogen.
If these factors all combine together and then persist for a few days, blue-green algae cells will accumulate in the surface layer of the waterbody and if the conditions persist for several days or more, then the cells can multiply to dramatic numbers, constituting a bloom. Blooms can persist for as long as the favourable conditions remain in place.
Are blooms of blue-green algae getting worse?
Blue-green algae have always been present in the river system and blooms are a natural phenomena. In 1830 Sturt recorded the Darling as tinged with green and tasting of vegetable decay. In 1878 the blue-green algae Nodularia spumigena bloomed in Lake Alexandrina causing the death of animals which drank the water. Blooms of blue-green algae in the River Murray in South Australia have been recorded intermittently since records began in 1947. In the Darling River in 1991 a toxic bloom of blue-green algae occurred over a distance of 1000km and caused the New South Wales government to declare a state of emergency. Blooms have occurred throughout 800km of the River Murray between Hume Dam and Euston in 1983 and 2009.
During very low flow periods, blooms are probably getting more intense and possibly becoming more frequent. The regulation of the River Murray system ensures that the river continues to flow through most summers when blooms would have been most likely. However prolonged dry periods with reduced flows, combined with the additional nutrients now present from eroded soils and waste discharges, means intense blooms are more likely.
What should be done when an algal bloom is found?
Blooms can start as small green floating dots and develop into thick, paint-like scums on the water surface. They are often green or blue-green in colour but can also be white, brown, blue, yellow-brown or red. Identification can be difficult, so if blue-green algae is suspected it is most important to avoid direct contact with the water and contact the appropriate council or water authority in that State. Then measures can be taken to examine and analyse the water for algae and if necessary alert users.
Information updates about blue-green algae blooms and Red Alert warnings can be obtained from the Regional Algal Coordinating Committee freecall Algal Information Hotline on 1800 999 457.
Contacts for blue-green algae blooms in the River Murray:
New South Wales Algal Information Hotline 1800 999 457
New South Wales Media contact - Bunty Driver 03 5898 3910
Victoria Blue Green Algae Hotline 03 5833 5785
South Australia – SA Water contact - Thorsten Mosisch 08 7424 1984
