This section provides an assessment of aquatic ecosystems and water quality in the ACT.
The main pressures on aquatic ecosystem condition in the ACT are land use impacts, modified river flows, and climate change
48% of assessed river reaches have poor to degraded riparian condition
Native species typically account for less than 30% of fish abundance in the Murrumbidgee River
Recreational water quality is poor for both lakes and rivers with closures at many sites due to enterococci and blue-green algae
Healthy aquatic ecosystems are essential to the ACT’s biodiversity, urban community, and agriculture. Aquatic ecosystems, and their riparian and floodplain lands, provide many environmental benefits and are habitat for both aquatic and terrestrial species. They provide ecosystem services such as the supply of water resources, water purification and nutrient cycling, and are important places for culture, recreation and social interaction.
Assessments of the ACT’s groundwater systems are not included in this report. Groundwater is a minor component of total water use in the ACT, and typically restricted to non-potable supply. There is also a lack of comprehensive data on groundwater resources and quality data in the ACT making difficult to assess their condition. The ACT’s State of the Environment 2015 report concluded that groundwater availability and quality were likely to be good in the ACT.Office of the Commissioner for Sustainability and the Environment, 2015, ACT State of the Environment Report 2015, ACT Government, Canberra. It was also concluded that the volume of groundwater extraction was far less than the recharge volume for aquifers.
Aquatic ecosystems in the ACT
The main rivers in the ACT region are shown in Figure W1, these are:
- Murrumbidgee River, which is the largest river flowing through the region and the second longest river in Australia. The river originates in the alpine area to the south of the ACT and is heavily influenced by water diversions from the Snowy Mountains Scheme. All rivers and creeks in the ACT drain into the Murrumbidgee River.
- Molonglo and Queanbeyan rivers, which originate to the south-east of the ACT and drain through Lake Burley Griffin before flowing into the Murrumbidgee River. The Queanbeyan River supplies water to the Googong Reservoir.
- Cotter River, which has a protected catchment and provides high-quality water to three reservoirs: Corin, Bendora and Cotter. The river originates in the Brindabella Mountains before flowing into the Murrumbidgee River.
- Gudgenby, Naas, and Paddys rivers are also significant rivers in the region.
Figure W1: Catchments and main rivers in the ACT region
Canberra has three constructed lakes – Lake Burley Griffin, Lake Ginninderra and Lake Tuggeranong – and numerous constructed ponds and wetlands. These lakes provide habitat for biodiversity, water pollution control, improve aesthetics and heat mitigation, and are sites for a range of recreational opportunities.
The ACT also has the Ramsar-listed Ginini Flats Wetland Complex in the Namadgi National Park, and 12 nationally important wetlands listed in the Directory of Important Wetlands in Australia (Figure W2).Environment Australia, 2001, A Directory of Important Wetlands in Australia, Third edition, Australian Government, Canberra, found at www.environment.gov.au/resource/directory-important-wetlands-australia, accessed August 2019. High Country Bogs and Associated Fens was added to the endangered category of the ACT Threatened Ecological Communities List in February 2019.
Figure W2: Significant wetlands in the Canberra region
Pressures on aquatic ecosystems
There are many pressures on the ACT’s aquatic ecosystems including changes in land use types, degradation of water quality, loss of riparian and other catchment vegetation, the alteration of natural flow regimes, modified river channels, streamflow diversion, fire, introduced species, and recreational fishing. Many of these pressures are rarely localised, with impacts usually affecting downstream ecosystem health. In the case of significant impacts, river degradation can be extensive. For example, the impacts of storage dams and their associated flow alteration on rivers can occur over extensive distances (see Case study: Impact of the Snowy Mountains Scheme on the Murrumbidgee River). This means that for those river systems that originate in NSW (Murrumbidgee and Molonglo Rivers), their condition within the ACT is highly influenced by upstream catchment conditions and management.
The main pressures on aquatic ecosystems are discussed below.
Land use and habitat loss
The clearance of vegetation and degradation of soils associated with modified landscapes such as urban and agricultural areas can significantly impact aquatic ecosystem health. Modified landscapes increase the pollutant and sediment loads entering waterways and alter hydrology through changes to natural drainage and river channels. The construction of large impervious surfaces in urban areas also increases surface run-off which can pollute waterways with fertilisers and other chemicals, organic matter, salts, soil, oil and sewage effluent.
The clearance and degradation of riparian zones has resulted in the loss of crucial habitat (including instream woody debris and terrestrial habitat) and functions such as shading, channel protection and food resources. Riparian condition has also been affected by loss of connectivity and the introduction of exotic species such as willow trees (see riparian connectivity in Indicator B4: Extent and condition of native vegetation.
Agricultural production can also have significant impacts on aquatic ecosystems. For example, native vegetation clearance for cropping and grazing has led to increased soil erosion and the potential for chemicals and animal waste to enter waterways. These compromise water quality through sedimentation, elevated nutrients, and the introduction of potentially toxic chemicals. Forestry activities can also impact on aquatic ecosystems, particularly through erosion and increased run-off following harvesting operations and the introduction of roads.
Water reservoirs and weirs cause significant alteration to the timing and volume of natural flow regimes and are barriers to the movement of fish and other species. Changes to natural flows are particularly detrimental for species with life-cycle stages that are intimately linked to seasonal flow changes. In addition to flow alteration, reservoirs can cause thermal pollution through the release of cold water which can impact on biodiversity. Other impacts on river flows include channel modifications to prevent the duration and frequency of flooding. Any alteration to river flows can change the natural morphology of rivers.
The impacts of modified flow regimes are compounded by the occurrence of drought. Extended periods of reduced flows can lead to increased water temperatures (especially where riparian vegetation has been cleared), degraded water quality and increased risk of algal blooms. These have negative consequences for biodiversity and agriculture (stock animals). Extended dry conditions can also result in habitat loss and depleted biodiversity on the edges of water systems.
Bushfires remove vegetation cover, exposing and altering the structure of soils and increasing the risk of significant erosion. Consequently, rainfall and run-off after bushfires can deposit large volumes of sediment and ash into aquatic ecosystems. These deposits degrade water quality by increasing turbidity and nutrient concentrations, and can reduce dissolved oxygen concentrations causing the loss of fish and macroinvertebrates. Large amounts of sediment and ash can also smother instream habitat.
Severe fires can also result in the loss of riparian vegetation and the habitat, shading and food resources that this vegetation provides.
In addition to biodiversity impacts, fires that occur in drinking-water catchments can have consequences for domestic water supply. These include increased water treatment costs and reductions in water yields due to increased uptake by regenerating vegetation.
Climate change exacerbates existing pressures on aquatic ecosystems. Reduced rainfall (including snowfall), hotter temperatures and increased evapotranspiration (see Climate change section) all have severe consequences, including:
- reduced river flows and reduced wetland inundation
- reduced deep water habitat refuges
- higher water temperatures and lower dissolved oxygen concentrations
- extended dry periods punctuated by severe storms which result in large nutrient, sediment and other pollutant pulses
- increased algal blooms, and
- more frequent and severe bushfires which compromise water quality and riparian vegetation.
Although the aquatic species of the ACT are well-adapted to extremes of floods and droughts, these events are projected to intensify under climate change, pushing some species and communities beyond their ability to adapt. In the long term, the pressures of climate change on freshwater ecosystems could lead to significant and long-lasting changes in the species present in rivers, lakes and wetlands in the ACT.
That the ACT Government:
identify opportunities to develop water-sensitive urban design measures to reduce the impact of urban land use on aquatic ecosystems.
re-establish riparian vegetation in both urban and rural areas to improve habitat and protect lakes and waterways from pollutant run-off.
establish a government reporting framework for the assessment of aquatic ecosystem health. This should include the selection of key monitoring sites that provide comprehensive coverage of land use types, sub-catchments and ecosystems across the ACT; incorporate work undertaken for the Catchment Health Indicator Program; incorporate all relevant condition parameters; and produce public reports at appropriate intervals to provide meaningful assessments.
produce an annual recreational water quality report that includes monitoring results, investigations into the main sources of pollutants, recommended actions to improve water quality; and assessments of management effectiveness.
increase fish-stocking programs to maintain fish populations in Canberra’s lakes and ponds.
identify opportunities to collaborate with the NSW Government on management activities to improve aquatic ecosystem health upstream and downstream of the ACT, including the management of native and alien fish, re-establishing riparian zones and reducing catchment erosion.
seek to increase water releases to the upper Murrumbidgee River under the Snowy 2.0 project to improve aquatic ecosystem health in the Murrumbidgee River.
Aquatic ecosystem health is variable across the ACT and strongly influenced by land use. Aquatic health is mostly good in conservation areas, but condition is poorer in urban and rural areas. The impact of land use is particularly evident for assessments of macroinvertebrate and riparian condition. Dry conditions in the region are also having an impact on aquatic health. Alien fish populations are high for the Murrumbidgee River with native fish accounting for less than 30% of fish abundance and 20% of biomass.
- ? Poor
- ? Fair
- ? Good
All river flows were well below the long-term average in 2017 and 2018. A continuation of these conditions will have consequences for the ecosystem health and amenity of rivers in the ACT. All discharges downstream of storage reservoirs met the environmental flow requirement; this took place despite the significantly reduced rainfall and river flows in 2017 and 2018.
Water quality was generally good for the reporting period, including for sites in urban and rural areas. Water quality results may reflect the decreased rainfall for most of the reporting period. However, turbidity remains an issue following high rainfall events. Water quality in the Murrumbidgee River is comparable upstream and downstream of the ACT indicating minimal water quality impacts in the region.
Recreation water quality is poor in the ACT for both lakes and rivers. Nearly every monitored recreation site experienced closures due to the exceedance of enterococci guidelines, and blue-green algae has required extended closures in Canberra’s lakes. Lake Tuggeranong was closed for most of the 2018–19 recreational swim season due to poor recreational water quality.
Indicator assessment legend
Environmental condition is healthy across the ACT, OR pressure likely to have negligible impact on environmental condition/human health.
Environmental condition is neither positive or negative and may be variable across the ACT, OR pressure likely to have limited impact on environmental condition/human health.
Environmental condition is under significant stress, OR pressure likely to have significant impact on environmental condition/ human health.
Data is insufficient to make an assessment of status and trends.
Adequate high-quality evidence and high level of consensus
Limited evidence or limited consensus
Evidence and consensus too low to make an assessment
Assessments of status, trends and data quality are not appropriate for the indicator
Aquatic ecosystem health 2015 to 2018
The main pressures on aquatic ecosystem condition in the ACT are land use impacts, modified river flows, and climate change.
Macroinvertebrate condition 2015 to 2018
Only 25% of reaches assessed were found to have good to excellent macroinvertebrate condition, 26% were found to be in poor to degraded condition, with 49% classed as fair.
Only 14% of reaches were assessed as having good to excellent riparian condition, 37% were found to be in fair condition and 48% were assessed as poor to degraded.
There are positive trends for some populations of native fish including the Two Spined Blackfish and Macquarie Perch in the Cotter River, and Murray Cod in some sections of the Murrumbidgee River.
Alien fish species are common in the ACT, with native fish typically accounting for less than 30% of total fish abundance and less than 20% of total fish biomass in the Murrumbidgee River. The dominance of alien species in the Murrumbidgee River is mainly due to high numbers
River flows 2015 to 2018
Water Quality 2015 to 2018
Recreational water quality 2016–17 to 2018–19
Nearly every monitored recreation site experienced closures due to the exceedance of enterococci (faecal coliform bacteria) guidelines.