Figure 6 Environmental Expenditure
	Note: 2005/06 and 2006/07 figures represent expenditure that was recorded as being for the primary purpose of environmental management. 2004/05 reported expenditure includes figures where the primary purpose of the activity was not limited to environmental management. Click to enlarge

Hydro Tasmania’s hydropower system affects aquatic systems as a result of both changing the flow regime and diverting water within and between catchments and subcatchments. The total volume of water diverted by Hydro Tasmania is estimated to be between one third and one half of all water used for energy production. There is a variety in length and volume of diversions throughout the system from substantial rivers to small canals. Information on catchments is available on the Hydro Tasmania website and includes diagrams showing significant diversions.

Aquatic Ecosystems

Low lake level environmental management
In 2006/07, low lake level monitoring programs were developed and implemented for Great Lake, Lake Echo and Lake King William. Risk bands had been established for specific lakes, based on potential environmental and social impacts that could arise when water levels are drawn down to below normal minimal operating levels for prolonged periods. Impacts could include recreational access restrictions, shoreline erosion, deterioration in water quality, loss of habitat, risk to threatened species and threats to operational infrastructure.

Environmental trigger values, derived from Australia and New Zealand Environment and Conservation Council (ANZECC) guidelines, were established for key water quality and ecological indicators. Monitoring of indicators was undertaken by Hydro Tasmania Consulting in conjunction with Inland Fisheries Service Biological Consultancy. Regular reporting ensured that management was alerted to changing conditions. Key stakeholders - Inland Fisheries Service, MAST and the public - were kept informed of conditions via reports, public notices and media releases.

As the water was drawn down to lower levels, monitoring results from Great Lake indicated a decrease in the distribution and abundance of charophyte beds, which are habitat for some threatened fish and macro invertebrate species, and an increase in turbidity and nutrient levels. Results from Lake Echo indicated an algal bloom in June while Lake King William showed
no deterioration.

The decision to decrease water levels into an environmental and social risk band is made at senior management level.

More information on low lake level management is available on our website.

Algal blooms

Lagoon of Islands
The Lagoon of Islands has been managed by Hydro Tasmania as a water storage in southern Tasmania to provide water to Ouse and Shannon River irrigators and riparian water users. Due to high nutrient input, water quality conditions in the lagoon have deteriorated, resulting in protracted algal blooms rendering the water unfit for the purpose.

Research and monitoring instigated in the previous reporting period has facilitated an understanding of the underlying causes of the poor water quality conditions. In 2006/07, a Nutrient Management Strategy was introduced that combines scientific and engineering solutions.

This strategy will be implemented over the next 20 years and will address the present algal bloom in the short-term, and reduce total phosphorus concentrations over the long-term. The strategy, estimated to cost $4.3 million over the next five years, aims to improve water quality and ecosystem health. Ecosystem responses to the management actions will be closely monitored as we move towards achieving more sustainable conditions in the lagoon.
See our website for more information.