The preservation and enhancement of Lake Burley Griffin as a central landscape feature, essential to the character and setting of the National Capital, is a matter of national significance in the planning and development of Canberra.
Lake Burley Griffin is an integral part of the tributary system within the Murray-Darling Basin, Australia's most significant drainage basin. Water management within the Basin is also a matter of national significance with Lake Burley Griffin acting as a retention pond for downstream parts of the system.
Lake Burley Griffin is also an important inland water resource that supports a variety of water-based commercial and recreational uses for Canberra's residents and visitors. This means that there is increasing pressure to provide better water quality outcomes to support these functions and to protect the health and safety of users.
The National Capital Authority is responsible for the management of the Lake. Sustainable use of the Lake is promoted whilst protecting and enhancing its water quality and allowing for a greater and more diverse range of uses.
Water quality is usually determined by reference to a number of factors, particularly turbidity and suspended material, phosphorus, nitrogen, algae and chlorophyll-a, conductivity and pH, bacteria, metals, and dissolved oxygen. At any point in time the water quality will vary within areas of the Lake. These water quality factors and variations across the Lake are influenced by a range of natural and man-made trends and activities, including:
- Climate – rainfall, temperature and wind conditions. For example, the ten year extreme drought conditions between 1999-2009 saw near zero catchment inflows to the Lake and a changing physical and chemical environment conducive to increases in blue-green algae.1
- Lake geography – water depth, slope of lake bed, aquatic plants, bank treatments, exposure to prevailing winds and inflows.
- Urban growth – since the Lake was formed some 48 years ago, the ACT population has increased from 70,000 in 1963 to 365,000 in 2011 (Australian Bureau of Statistics, 2011), resulting in an increase in urban stormwater and other discharges of nutrients and organic material.
- Activities in the catchment – water treatment plants, water abstraction, operation of dams, agriculture, horticulture, mining land uses, plant and animal populations, lake use.
1 The Lake Burley Griffin Water Quality Monitoring Report July 2010 – June 2011 (Australian Laboratory Services Water Resources Group Canberra, 2011) noted that conditions in the Lake appear to have improved over the preceding drought period with blue-green algal counts at beach sites showing a considerable decrease compared to 2009.
Parameters set out in the ANZECC/ARMCANZ Australian and New Zealand Guidelines for Fresh and Marine Water Quality (2000), Guidelines for Managing Risks in Recreational Water (Australian Government, 2008), local guidelines and water-quality data collected over the past 28 years have been used to develop the benchmarks for the Water Quality Management Plan (WQMP) contained in this document.
The ANZECC/ARMCANZ (2000) guidelines are generic for south-east Australian waterways and include guidelines for all uses—including drinking, recreational, irrigational and environmental uses. ANZECC/ARMCANZ (2000) also states that its generic guidelines can be modified to suit local conditions, if detailed local information is available.
In summary, the general water quality trends for Lake Burley Griffin over the period 1981-2009 indicate:
- The overall environmental health of the Lake is generally good.
- Turbidity has decreased and now remains in a consistently lower range. Drought conditions have probably been a factor in producing these low levels.
- Phosphorus concentrations have gradually decreased in the Lake, probably because of improved catchment management including improvements to sewage treatment plant discharge from the Queanbeyan Wastewater facility, and low inflows because of drought since 2002.
- Nitrogen concentrations have also decreased gradually, but not as markedly as phosphorus. The decrease in both nutrients has probably been due to the same factors.
- Total algal cell concentrations have remained within the same general range, with cyanobacterial cell concentrations generally below the high alert level for recreational exposure according to the Australian Government (2008) and ACT Government (2010). However, the intensity of late summer cyanobacterial blooms has increased in recent years.
- Chlorophyll-a values have decreased and all primary water contact areas are now generally below the benchmark values for other ACT waters (ACT Government, 2011).
- Conductivity had remained relatively consistent prior to 2003. However, since December 2002, there has been an upward trend. This is likely to be due to drought conditions.
- pH values have remained in the same general range, and within an acceptable limit for this type of water body.
- Bacterial counts have generally remained within the guideline values but have had some significant exceedences of undetermined cause.
- The Lake contains high levels of some metals, particularly in the sediments.
- Averaged dissolved oxygen concentrations were at their maximum during the late winter months, and at their minimum during the late summer months.
There is a considerable amount of local information available on Lake Burley Griffin water quality. This has been invaluable in setting appropriate benchmarks for the WQMP and in setting management practices to achieve those benchmarks. The WQMP lists commonly occurring events that can reduce water quality and outlines management measures to protect public health and the environment.
The WQMP is designed to be a practical guide to actions required for the effective management of the Lake's water quality. It fits within the overarching direction of the Lake Burley Griffin Management Plan. This WQMP will be revised and updated regularly as new information becomes available.