Background: Water

Water underpins almost every aspect of life and is a vital resource for ecosystems, landscapes and communities across the globe.

Healthy aquatic ecosystems are essential for biodiversity, agriculture and community amenity. Along with their riparian and floodplain lands, aquatic ecosystems provide many environmental benefits and are habitat for both aquatic and terrestrial species. They also 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.

Aquatic ecosystems in the ACT

The main rivers in the ACT region are shown in Figure 1. These are:

• The 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.
• The 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.
• The 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.
• The Gudgenby, Naas, and Paddys rivers are also significant rivers in the 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 2).^[1] High Country Bogs and Associated Fens was added to the endangered category of the ACT Threatened Ecological Communities List in February 2019.

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 Impact of Tantangara Dam on the Murrumbidgee River flows). 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.

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.

River flows

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.

Fire

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.

For more information see Fire. 

Climate change

Climate change exacerbates existing pressures on aquatic ecosystems. Reduced rainfall (including snowfall), hotter temperatures and increased evapotranspiration 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.

For more information see Climate change. 

Background to indicators

Indicator W1: Aquatic ecosystem health

Assessing ACT’s aquatic health – the Catchment Health Indicator Program (CHIP)

The Catchment Health Indicator Program (CHIP) provides a score of catchment health in the ACT region using data collected by Waterwatch volunteers and staff. Assessments include monthly water quality data, macroinvertebrate (water bugs) abundance and diversity collected twice a year from key sites, and riparian vegetation assessments conducted every two years. When combined for an individual stretch of waterway (a reach), these data produce a score that indicates the overall health of that reach. A reach only receives a score if the minimum data requirement is met.

Assessments are accompanied by a report card supplied by the local Waterwatch coordinator to provide expert knowledge on condition results and possible issues. The report cards ensure that vitally important context is provided by the coordinators who know the underlying geology, hydrology, land use and history of the catchments.

It is important to note that the site selection used for CHIP has a significant influence on the overall number of reaches assigned to a particular condition score. For example, having a high proportion of survey sites in urban areas will likely mean a higher total of sites in poorer condition categories. Consequently, although figures on the number of reaches in each condition category may be useful for an overview of CHIP results, they should be viewed with caution. It is more appropriate to compare changes in individual reach condition over time, than to make comparisons between different reaches and catchments.

Information on reaches used for CHIP assessments, including individual condition scores, characteristics and location, and the main pressures affecting condition, can be found in annual CHIP reports.

Macroinvertebrates

Aquatic macroinvertebrates are a diverse group of insects, crustaceans and molluscs that include dragonflies, stoneflies, snails, yabbies, water boatmen and worms. They are relatively sedentary and spend at least part of their life in aquatic ecosystems. Macroinvertebrates are critical to aquatic ecosystem health because they are an important food source for fish and other species such as platypus, and are critical to ecosystem processes such as nutrient cycling.

Because macroinvertebrates are widespread, easy to sample and sensitive to a range of pressures, they are routinely used as indicators of the condition of aquatic systems and their surrounding catchments. Land use change, aquatic and riparian habitat modification, water pollution, and river regulation all affect macroinvertebrate community health.

The CHIP assesses macroinvertebrate community health for each reach using the results of two annual surveys from key sites. The assessment methodology can be found in annual CHIP reports.

Riparian condition

The riparian zone is the land and vegetation that fringe aquatic ecosystems. They are vital for aquatic health as these zones provide habitat, stable banks, shade, buffers and filters for incoming run-off, reducing sediments, nutrients and pollutants, and food for aquatic species. The loss and degradation of riparian zones compromises both aquatic and terrestrial biodiversity.

Riparian zones are particularly important during drought periods, providing refuge for terrestrial species and helping to reduce the impacts of low flows on aquatic systems. Riparian vegetation is often the only native vegetation remaining in heavily modified landscapes, making them vital wildlife corridors. The health of riparian zones is often dependent on river flows with many riparian species requiring regular flooding for regeneration. Changes to natural flow regimes and the increased occurrence of drought has significantly reduced the flooding of riparian zones, leading to a decline in riparian vegetation health.

The CHIP assesses riparian condition for each reach with surveys conducted every 2 years. The assessment methodology can be found in annual CHIP reports.

Native fish

The distribution and abundance of native fish is highly dependent on the condition of aquatic ecosystems. Pressures on native fish include:

• alteration and reduction of natural flow regimes,
• structures such as dams, road crossing and weirs that create barriers to the movement of fish,
• degraded habitat including loss of riparian vegetation,
• invasive fish species which place pressure on native fish through predation, competition for habitat and resources, disease and habitat modification,
• degraded water quality, and
• recreational fishing, particularly unregulated (unlicensed) fishing, which impact on species already affected by other pressures.

Connected waterways are critical for the survival of native fish. Structures such as dams, weirs and road crossings create barriers that can prevent fish passage. Native fish move within and between waterways to breed and to locate critical resources such as food, shelter, nursery sites and spawning grounds. Native fish species can also utilise different parts of river systems for different life cycle stages. For example, the Murray Cod (Maccullochella peelii) and Golden Perch (Macquaria ambigua) usually travel upstream to find suitable breeding areas. Barriers that prevent fish passage can also cause populations to become isolated, which can lead to inbreeding and loss of genetic diversity.

The ACT Government stocks juvenile Murray Cod and Golden Perch into Canberra’s lakes and larger ponds including Lake Burley Griffin (funded by the National Capital Authority), Lake Ginninderra, Lake Tuggeranong, the Yerrabi in Gungahlin, Upper Stranger, Point Hut, West Belconnen and Coombs ponds. Stocking is undertaken to provide recreational fishing and to increase the abundance of native species. The lakes and ponds do not provide the required environmental conditions for the successful breeding of Murray Cod and Golden Perch and so populations must be maintained by regular stocking. Stocking of urban lakes and ponds also aims to reduce the angling pressure on natural riverine populations, such as the Murrumbidgee fish population.

Indicator W2: River flows

The ecological condition and functioning of rivers are strongly linked to natural flow regimes. A flow regime is the timing, size and duration of river flow events. It is a key driver of river and floodplain wetland ecosystems, influencing river morphology, biodiversity, and the processes that sustain aquatic ecosystems. Modification of natural flow regimes may affect biodiversity, alter riverine habitat, and facilitate the invasion of exotic species. Aquatic plant and animal species have evolved life histories directly in response to the natural flow regimes. Healthy river flows are also required to support human activities and needs such as domestic water supply, irrigation and recreation opportunities.

In the ACT, natural flows have been altered by water resource development such as the presence of dams and other barriers, regulation of flow, diversion or extraction of in-stream flows, and channel modification. Rainfall interception for farm dams can also impact on natural flows but this is minimal in the ACT with farm dams estimated to reduce run-off to surface water by approximately 1%.^[2]

Land use also influences river flows; for example, highly urbanised catchments and cleared agricultural lands can quickly increase river flows due greater rainfall run-off. Other impacts on river flow include fire and plantation forestry. These activities can both increase and decrease flows through the removal of vegetation which increases rainfall run-off, and regeneration which increases the uptake of water.

The natural flows in ACT rivers are highly variable, characterised by generally dry conditions punctuated by wet years which replenish water storages and river systems. Flows also vary seasonally with higher flows usually occurring in the winter and spring months.

For information on the impact of the Snowy Mountains Scheme on the Murrumbidgee River see case study on the impact of Tantangara Dam on the Murrumbidgee River flows.

Environmental flows

Environmental flows describe the quantity and timing of water required to maintain the health of aquatic ecosystems affected by water resource development. In the ACT, environmental flow requirements are specified in the Environmental Flow Guidelines, an instrument under the Water Resources Act 2007.

In heavily used river systems, such as water supply catchments, environmental flows can be delivered in ways that protect specific components of the flow regime, to help keep stream ecosystems healthy, or to provide conditions required for aquatic fauna life histories (such as fish breeding). Environmental flows can be provided through releases and spills from reservoirs (for example, the Cotter, Murrumbidgee and Queanbeyan rivers) and through restrictions on the amount of water that can be withdrawn.

Indicator W3: Water quality

Water quality is critical to the ecosystem services that rivers provide for a range of social, economic and environmental needs. Good water quality is required for drinking water, aquatic ecosystem health and the biodiversity it supports, as well as for recreational and cultural opportunities. Poor water quality can lead to the loss of aquatic species, human illnesses, and the loss amenity from the closure of recreational water bodies and odour. Degraded water quality can also increase the cost of water treatment and prevent agricultural activity.

Water quality is highly sensitive to a range of factors including land use, flow regimes, and the loss of riparian vegetation. Land clearing for agriculture and urbanisation has increased erosion, sedimentation, turbidity and salinity, as well as the increased run-off of a range of pollutants. Agricultural use of chemicals and fertilisers has increased concentrations of nitrogen and phosphorus in waterways, as well as concentrations of herbicides and pesticides. Other pressures on water quality include fire and the impact of invasive species such as carp and willow.

Limitations of current water quality monitoring

Routine water quality monitoring (based on set time intervals) often misses significant pollution events. For example, water quality can change quickly in response to the prevailing conditions within a catchment, and pollutant loads can decrease rapidly after events occur. This means that high levels of pollutants from stormwater runoff events are unlikely to be detected by routine monitoring unless, by chance, sampling is undertaken during or shortly after such an event. Consequently, the results of routine monitoring are often biased toward more favourable water quality assessments, rather than reflecting the actual condition of water quality and catchment pressures.

Therefore, water quality monitoring undertaken at regular intervals, mostly monthly in the ACT, is not sufficient to accurately assess water quality. To understand the sources and volume of pollutants, more frequent monitoring needs to occur, as well as events-based monitoring that assesses periods of high pollutant loads.

For more information see the 2022 investigation into the State of the Lakes and Waterways.

Water pollutants

Sources of water quality pollutants can be broadly classified as point (directly from industry and treatment plants) or diffuse (run-off from catchments). Following significant improvements in the regulation of point source pollution, diffuse sources are the major cause of water pollution. For example, the Canberra urban environment discharges treated sewage effluent from the Lower Molonglo Water Quality Control Centre; however, the high level of wastewater treatment means that pollution from unregulated diffuse sources remains the major cause of poor water quality in the ACT.

The main water quality issues in the ACT are:

• Turbidity and sedimentation: erosion is the main cause of turbidity and sediment problems, with significant occurrences following storms and bushfires. Turbidity reduces light penetration affecting the ability of aquatic plants to photosynthesise and impairing animal activities such as predation. At very high levels, suspended sediment can clog and damage fish gills and the filter-feeding apparatus of animals such as mussels. Large-scale sediment deposition can smother river habitats creating shallow flow areas that are subject to greater temperature extremes and the risk of invasion by aquatic weeds.
• Nutrients: although nitrogen and phosphorus are essential plant nutrients, elevated concentrations can cause excessive plant growth (eutrophication), including toxic algal blooms. Nutrient enrichment affects aquatic communities by changing species composition and reducing dissolved oxygen concentrations as a result of algal blooms. The major cause of increased nutrient levels is run-off from urban and agricultural catchments, particularly in areas with high fertiliser usage. Point sources of pollution, such as discharges from agriculture, industry and wastewater treatment plants, have also elevated concentrations of phosphorus and nitrogen.
• Salinity: the salt concentration of water presents a direct threat to aquatic ecosystems. While some aquatic species tolerate a range of salt concentrations, changes in salinity can kill a wide range of plants and animals. Human settlements are also affected by salinity because it accelerates corrosion and can damage infrastructure, such as roads and bridges. It also affects soil, plant and livestock health and can therefore reduce agricultural productivity. In the ACT, increased electrical conductivity in some areas may be caused by the underlying natural geology of the catchments.
• Dissolved oxygen: the concentrationofoxygen in the water is important for the maintenance of aquatic organisms. Low oxygen levels can stress fish, which can lead to fungal infections and disease, or result directly in the death of fish and other aquatic species. Dissolved oxygen concentrations are particularly affected by temperature (colder water can hold more dissolved oxygen), and severe declines occur following algal blooms.

For more on water quality see Expert commentary: Water quality in the ACT.

Indicator W4: Recreational water quality

Recreational water quality refers to the suitability of water for swimming and other activities that involve direct contact with the water. Canberra’s lakes and rivers are important for providing amenity and opportunities for recreation. However, the use of lakes and rivers depends on having good recreational water quality.

Assessments of recreational water quality are based on the potentially harmful bacteria known as enterococci and blue-green algae (cyanobacteria). Enterococci, also known as faecal coliform bacteria, are not necessarily a problem for aquatic ecosystems, as they generally serve as food for aquatic organisms without causing them harm. However, the presence of high numbers of faecal coliforms can affect human health when recreational activities involve direct contact with the water. Ingestion of these bacterial pathogens can lead to gastrointestinal illnesses such as diarrhoea. Stormwater run-off is the main source of enterococci, with sewage overflows and releases from damaged pipes also potential sources.

Blue-green algae are naturally present in aquatic ecosystems, but under certain conditions their populations can increase causing a potentially toxic bloom. Low river flows, high temperatures and high levels of nutrients are the primary cause of blue-green algal blooms. Blue-green algae can produce toxins that are harmful to humans and animals when they are swallowed, inhaled, or come into direct contact with the skin. Reactions are variable, depending on the length and type of contact. Common symptoms include irritated skin, flu-like symptoms and gastrointestinal illness resulting in vomiting, diarrhoea, fever and headache. Urban and rural run-off is also the main driver of recreation closures due to blue-green algae. Rainfall run-off transports high amounts of nutrients into lakes and other waterways enabling algal blooms to occur.

The occurrence of algal blooms is also driven by climate factors such as extended dry periods and hotter temperatures. With these conditions projected to increase in the future (see Climate change), reducing the amount of nutrients in waterways will be required to prevent longer and more frequent recreation closures in the future. The prevention of blue-green algae blooms will not only increases the amenity of the ACT’s lakes and waterways, but also prevents potential impacts on aquatic ecosystems such as fish kills.

To reduce the number and duration of recreational closures, there needs to be improved run-off management and interception in urban areas, and the re-establishment of riparian vegetation in both urban and rural areas. For more information see Expert commentary: Water quality in the ACT.

Recreational water quality monitoring

Recreation water quality monitoring is undertaken in accordance with the ACT Guidelines for Recreational Water Quality across a total of 17 sites in Lake Ginninderra, Lake Tuggeranong and the Murrumbidgee, Paddys and Molonglo rivers. Recreational water quality is also assessed at 10 sites in Lake Burley Griffin by the National Capital Authority. Although the ACT Government is not responsible for the management of Lake Burley Griffin, this data is included because of the important amenity and recreational value of the lake to Canberrans.

Water samples are taken weekly during the recreational swimming season (between approximately October to April) for enterococci and throughout the year for blue-green algae. If samples for enterococci and blue-green algae exceed guideline levels, then a resample is obtained and tested. If two consecutive samples exceed guideline levels, then the site is closed for primary contact. Reopening a recreational site after a closure requires two samples within guideline levels.