BLUE-GREEN ALGAE AND COMMONWEALTH ENVIRONMENTAL WATER

This statement provides an overview on blue-green algal blooms and how they are managed, including the role of the Commonwealth Environmental Water Holder.

KEY POINTS

  • Blue green algae are a natural occurrence in freshwater ecosystems. Blooms can occur in response to favourable conditions, which include still or slow-flowing water, abundant sunlight, hot temperatures and sufficient levels of nutrients.
  • Blue green algal blooms are not caused by the delivery of environmental water.
  • Once a blue-green algal bloom forms, very little can be done to stop it. The scale of the current events means that the provision of additional flows would be unlikely to significantly affect the blooms.
  • The management of blue-green algal blooms is a responsibility of state government agencies and local waterway managers. In the Murray catchment, joint government arrangements exist, which are overseen by the Murray Regional Algal Coordinating Committee.
  • The Commonwealth Environmental Water Holder is in regular (often daily) contact with local waterway managers. The Commonwealth Environmental Water Holder closely monitors the latest information on blue-green algal blooms and is prepared to respond should practical interventions using environmental water be identified.
  • The Commonwealth Environmental Water Holder is investigating whether there are opportunities to use the limited volumes of environmental water available to provide refuge habitat for aquatic species (particularly if the decay of the algal bloom leads to low oxygen levels in the waterways).

BACKGROUND

What are blue-green algal blooms?

Despite their name, blue-green algae are a type of bacteria. They are a naturally occurring component of freshwater environments.In fact, they are an essential part of a healthy body of water, as they produce oxygen and are themselves a source of food for certain aquatic animals.

In response to favourable conditions, they may undergo population explosions, called blooms. These conditions include still or slow-flowing water, hot days with abundant sunlight and sufficient levels of nutrients (especially nitrogen and phosphorus).

Blue-green algal blooms occurred under natural conditions. In 1830, the explorer Charles Sturt recorded the Darling River as tinged with green and tasting of vegetable decay. In 1878, blue-green algae bloomed in Lake Alexandrina causing the death of animals that drank the water. However, an analysis of monitoring data collected over the past 30 years indicates that there are increasing concentrations of blue-green algae in the Murray system and there has been an increase in the duration of individual algal blooms at upstream sites[1].

Problems caused by blue-green algal blooms

When blooms of blue-green algae occur they interfere with other uses of the water, 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 scum.

Blue-green algae can be toxic. Contact with high concentrations of blue-green algae can cause skin and eye irritations. In severe cases, the toxins can cause damage to the liver and nervous system. Exposure to algal toxins has been linked to fatalities of livestock, wildlife and pets.

As the bloom subsides, the dead and decaying algae can reduce the oxygen levels in the water, causing stress or death to aquatic animals. During periods of drought, aquatic ecosystems can be severely degraded by algal blooms.

Managing blue-green algal blooms

Once a blue-green algal bloom occurs, very little can be done to stop it. Blooms can persist for as long as the favourable conditions remain in place—so good rain, cooler weather or less sunshine will reduce blue-green algal blooms over time.

Frequent testing of toxicity can help to assist water-use decisions and identify alternate water supplies for stock and domestic uses, as necessary. Drinking water supplies undergo additional treatment to remove dissolved toxins and make the water safe for consumption. Public alerts are issued to ensure all water users are aware of problems and to inform them to avoid direct contact with the water.

Algal blooms are most effectively managed at the local level because of the varying circumstances in each case. Local councils and state water authorities are best placed to investigate suspected outbreaks and alert the public of any unsafe waters.Each state government has extensive monitoring arrangements in place to detect and measure algae, as well as comprehensive emergency plans for dealing with algal blooms.

In the Murray catchment, there are long standing arrangements between Basin state governments for handling algal bloom outbreaks. The response is coordinated through the Murray Regional Algal Coordinating Committee, which comprises of members across a range of agencies, including state government water and health agencies, river operators, irrigation authorities, local governments and natural resource management agencies.

The role of the Commonwealth Environmental Water Holder

The Commonwealth Environmental Water Holder is responsible for managing environmental water that has been acquired by the Australian Government. This water must be used to protect and restore the environmental values of the Murray-Darling Basin.

The Commonwealth Environmental Water Holder closely monitors the latest information on blue-green algal blooms and stays in regular contact with local water way managers. As noted above, there are limited options available to mitigate blooms, once they occur. Providing higher flows are unlikely to have a significant effect on large-scale algal blooms—the volumes and flows required to disperse blooms are often beyond what can be delivered in regulated systems. There may be opportunities to flush smaller-scale systems, however, any decision to do so would need to consider the risk that this would simply move the problem into another river system.

There may also be opportunities for environmental water to be used to create refuges of better quality water to protect native fish populations, particularly if a blackwater event (that is low levels of dissolved oxygen in the waterway) occurs once the algal bloom begins to decay. This can however be complicated if the sources of additional water (e.g. the reservoir from which environmental water is released) is also affected.

Environmental water is also being used to improve the overall resilience of the ecosystems—that is, ensuring the rivers and wetlands are in good health so they can withstand the short-term effects of events such as blue-green algal blooms.

This is consistent with the Commonwealth Environmental Water Holder’s obligations under the Basin Plan. The Basin Plan includes:

  • water quality objectives, including for water-dependent ecosystems
  • water quality targets for managing flows, which include targets relating to blue-green algae.

Like other state and federal water management agencies, the Commonwealth Environmental Water Holder must consider these targets when making decisions about using water.

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