The bloom as it happened
By Dr. Willis
A large bloom of blue-green algae started in Lakes Hume and Mulwala and continued downstream from Albury-Wodonga to Swan Hill and beyond. It is still present in high quantities and water access is controlled, with water use rationed in many towns supplied from the Murray, as drought conditions have reduced alternative water sources.
A combination of above average temperatures and low rainfall, with nutrients available, are ideal conditions for blue-green algae growth, and this El Nino summer has been extra hot. Unusually this bloom is of the species Chrysosporum ovalisporum, which is typically not common.
C. ovalisporum can produce the toxin cylindrospermopsin, which is a hepatotoxin, causing liver and kidney damage. Fortunately this bloom has low toxicity, consisting of mostly non-toxic strains. The affected water is more easily treated than other blue-green algae toxins, and can be completely destroyed with chlorine. Avoiding contact and ingestion of the untreated water is always the safest option.
Management authorities can take action to reduce blooms. In this case, water is being released from Lake Hume to help keep the river flowing and reduce the bloom. The bloom will disappear slowly once the water temperature drops, but a big rain fall is needed to quickly destroy the bloom and reduce the biomass present.
Alerts and local information is available from Water NSW.
What caused the bloom and how can we stop them in the future?
The occurrence of blue-green algae blooms are likely to increase with the increasing temperatures associated with climate change. However, high temperatures are only part of a suite of environmental factors that allow for large blooms of blue-green algae to develop, and suggest ways of preventing blooms. Nutrients, light and water stability are also important and the surrounding landscape can affect these factors and the health of the water system. Improving the surrounding environment can help protect water systems from cyanobacteria blooms.
Nutrients are food for cyanobacteria and without them they cannot grow. Reducing nutrient availability can be achieved by improved use of fertilisers on land to decrease run-off. Keeping livestock out of creeks and rivers and improving riparian vegetation can also improve the stability of the soil and reduce nutrients entering the water.
Cyanobacteria growth occurs more readily when the water is still and calm, making sure enough environmental water is available to maintain flows in a river will also help reduce blooms.
Climate change will not only affect temperatures but light (clouds) and rainfall as well. Changes in conditions can lead to different species blooming or changes in the strains – some of which can be more toxic than others. As this Murray River bloom demonstrates species that previously only occurred in small numbers may become dominant. Producing different toxins and potentially requiring different or additional treatment.
The 400 km stretch of green Murray River is a wake up call to society and managers that we need to be taking appropriate action now to restore riverside vegetation and allow environmental flows to avoid these events in the future.