Toxic algal blooms – a sign of rivers under stress
Box 1 | Is Newcastle's water vulnerable to toxic algal blooms?
Newcastle and surrounding towns in the Hunter Valley of New South Wales draw their water from several sources. One is the Chichester Dam located at the junction of the Chichester and Wangat Rivers. The catchment for this storage is mostly forest, and no problems with blue-green algae have ever been recorded.
Another source is the Grahamstown Reservoir, which is filled largely by water taken from the Seaham Weir on the lower Williams River. This reservoir supplies about 60 per cent of the water consumed in the cities of Newcastle and Lake Macquarie.
The Williams River recorded blue-green algae blooms in three consecutive summers between 1991 and 1993. Grahamstown Reservoir also experienced a bloom in February 1992. While these outbreaks did not pose an immediate health risk to people, they provided a warning that the region's water supply is vulnerable to toxic algal blooms.
Emergency measures
Land and water managers in the Hunter Valley have taken several steps to limit the impact of toxic algal blooms.
One important measure is water monitoring. The presence of potentially toxic blue-green algae species in the Newcastle water supply is monitored on a weekly basis at Grahamstown Reservoir and Chichester Dam and fortnightly in Williams River.
A contingency plan has been prepared in the event that an abnormal level of potentially toxic blue-green algal cells is detected. Water from the Grahamstown Reservoir will be filtered by a substance known as granulated activated carbon, which will remove toxins. If necessary, the Grahamstown Reservoir will be taken off-line and substituted by water from a subterranean supply. At extremely high levels of blue-green algal cells, the reservoir will be closed to recreational use.
Prevention is better than cure
While such measures are necessary to protect the Newcastle water supply in an emergency, they address the symptoms, not the causes, of toxic algal blooms. Longer term options must also be pursued to reduce the risk of blooms occurring in the first place.
Perhaps the main reason that the Williams River and Grahamstown Reservoir are vulnerable to algal blooms is the way in which the land and water are managed in the catchment area. The Williams River flows through agricultural and pastoral areas and through several rural townships. Farm run-off and township effluent are major sources of phosphorus which, when present in the river at sufficient concentrations, can lead to a toxic algal bloom.
In a recent inquiry into the health of the Williams River, the NSW Healthy Rivers Commission recommended that a number of actions be taken to ensure the continued health of the river system. These included the fencing of streams to prevent trampling by animals, the rehabilitation of banks and streams, and limits on water use.
The Williams River Total Catchment Management Committee is working with water users, farmers, government agencies and industry throughout the catchment to help bring about improvements in the way we use both the land and the water. Hopefully, a cooperative approach will ensure that the region's water remains good enough to drink.
Boxes
Box 2. Cyanobacteria: the simple things of life
Box 3. Harmful effects of blue-green algae on human health
Related sites
Algal information (NSW Government Department of Primary Industries, Office of Water)
What causes algal blooms (NSW Government Department of Primary Industries, Office of Water)
Page updated February 2012.