Source: Richie Southerton

10. Water

10.2 ACT trends

This section looks at trends for the following water topics:

What are the main water findings from the 2023 ACT State of the Environment Report? Watch the video and see the infographic below to find out.

The health of the ACT’s aquatic ecosystems

The ACT’s aquatic health is assessed using the Catchment Health Indicator Program, or CHIP for short. This program assesses catchment health in the ACT region using data collected by Waterwatch volunteers and staff. Assessments focus on water quality, the abundance and diversity of macroinvertebrates (water bugs), and riparian vegetation. This information is collected for an individual stretch of waterway (known as a reach), then the findings are combined to give that reach an overall health score. You can learn more about CHIP, or get involved with your local Waterwatch group by visiting the WaterWatch website.

CHIP results show that overall, the ACT’s aquatic ecosystem health is considered fair in urban and rural areas and good to excellent in conservation areas. This shows that the condition of aquatic ecosystems is strongly influenced by land use. There are some urban areas in good health, which shows that with careful management and use of water sensitive urban design, it is possible to live in harmony with our waterways. Water sensitive urban design is the way of planning urban areas to protect aquatic ecosystems and prevent flooding. This is done by minimising water runoff and reducing the amount of pollutants entering our waterways. Water sensitive urban design also aims to use rainwater runoff wisely to improve our urban environment.

This map shows the overall Catchment Health Indicator Program score for an individual stretch of waterway (known as a reach) in the ACT. Each of the coloured dots on the map show the average score from 2019 to 2022, from excellent to poor. Results show that aquatic health is strongly related to land use with most of the good to excellent scores in conservation areas, and fair condition scores mostly situated in urban and rural areas.

Data sourced from: Upper Murrumbidgee WaterWatch.

Threats to aquatic ecosystems in the ACT

Aquatic ecosystem health is dependent on the quality of our land and ecosystems, and the amount of water flowing into our rivers, lakes and wetlands. This means that climate change, land clearing, and highly modified landscapes such as urban and agricultural areas are the main threats to aquatic ecosystem health in the ACT. Bushfires are also a significant threat to river health and the quality of water in our reservoirs, and introduced species are threatening native fish. Poor aquatic health can impact on our biodiversity as well as make it unsafe for activities such as swimming, boating and fishing.

The main threats to the ACT’s aquatic ecosystems are discussed below.

Climate change

Climate change is causing drier periods and longer droughts (see Climate change section), making rivers and lakes stagnant, and killing plants and animals in our aquatic ecosystems. Climate change is also increasing storms and floods, eroding waterways and washing more pollutants into rivers, lakes and wetlands.

The Critically Endangered Corroboree Frog is threatened by climate change. Photo: Murray Evans.

Urban development and agriculture

When we clear natural environments to be used for urban development, farming or forestry, we remove native vegetation. The removal of native plants, especially riparian plants, results in the loss of nature’s filtration system and soil cover. This means the water flowing into rivers, lakes and wetlands is not as clean. When fast-flowing water runs over exposed land or concrete surfaces, without soaking in, it carries soil (also known as sediment) and chemicals with it.

Sediment entering Deep Creek from construction
areas in Whitlam, February 2020.
Source: ACT Waterwatch.

Urban and agricultural areas produce many pollutants including sediment, fertilisers and nutrients like nitrogen and phosphorous, chemicals, salt, oil and sewage. These pollutants can damage aquatic health. For example, large amounts of sediment can smother river beds and nutrients can cause algae and other aquatic plants to grow at unnaturally high levels limiting the light and oxygen available to underwater species. Some types of algae (such as blue-green algae) are toxic, making it unsuitable for people to drink or use for recreation.

We need to minimise the impacts of urban development on the environment, including on our waterways. This means that we need to protect as much existing native vegetation as possible, especially in riparian areas. We also need to greatly reduce the amount of sediment and other pollutants from entering our waterways, both during and after land development. This can be done by building wetlands and ponds to help clean up polluted water before it flows downstream. Even better is to avoid developing new areas of land altogether, and build within our existing urban area instead. For more, see Canberra’s growing urban area.

Fire

Bushfires burn the vegetation that protects soil from erosion. Rain can then wash the ash, soil and other water pollutants into waterways and reservoirs. This can lead to very turbid (muddy) and polluted water causing the death of some aquatic species such as fish and aquatic insects. The 2020 bushfires strongly impacted water quality and aquatic biodiversity in the ACT. For more information see Bushfires in the ACT.

Ash and sediment in the Cotter River after the Black Summer bushfires. Source: Mark Jekabsons.

Introduced species

The ACT’s waterways are threatened by introduced animal species, such as carp. These fish can dominate a natural ecosystem, meaning native fish must compete for food and habitat. Invasive fish numbers are high in the Murrumbidgee River; typically, less than a third of the fish in this large and important river are native. Plants such as willows can take over riparian zones and can clog rivers when they drop their leaves. Willows can slow and divert water flow with their extensive root systems, making aquatic ecosystems unsuitable for native species.

Carp, an invasive species impacting native fish. Source: Environment, Planning and Sustainable Development Directorate.

Changes in river flow

A river’s flow may change for a number of reasons. Drought reduces available water, and erosion changes where and how the river moves through the land. River flow can also be changed by humans through the building of dams, weirs and other structures.

Aquatic species rely on plentiful water in rivers to breed, develop and migrate. If there is not enough water, their numbers will decline. Plant species that need regular flooding events also decline if water flow is too restricted. Whilst native species have adapted to natural variation in flows, long-term drought conditions put considerable stress on aquatic ecosystems and biodiversity.

This graph shows how annual river flows (the total water that flows down a river in a year) can vary from the long-term average in response to rainfall. The graph shows river flows in relation to their long-term averages – 100% means that flows are average, but lower than 100% means a drier year, and over 100% means a wetter year. For years 2017 to 2019, flows were well below average, which put significant stress on aquatic species. For years 2021 and 2022, flows were well above the long-term average which is good for river health.

Data sourced from: Environment, Planning and Sustainable Development Directorate.

Dams and river flows

Humans have built dams, created river channels and diverted rivers to supply water for people, agriculture and industry. While these activities have made clean water available in our homes, they can harm the environment.

Dams, while vital for supplying water for drinking and food production, collect water that would otherwise flow into river systems. In drought years, dams can make ecosystems downstream dry out and die. This is why scientists have determined ‘environmental flows’. An environmental flow is the amount of water needed by an ecosystem and its species to function. Environmental flows are used to manage how much water is released from dams.

The presence of dams means that the ACT’s river flows are well below what has been considered a ‘normal flow’ in the past. This is particularly true for the Murrumbidgee River. Tantangara Dam in NSW captures flows from the upper Murrumbidgee River and diverts them for hydroelectricity and irrigation (water for agriculture). Today, only 10% of the Murrumbidgee’s natural flows are released from Tantangara Dam.

The Cotter Dam. Source: Mark Jekabsons.

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 recreation and provide places to cool down on hot summer days. Our use of lakes and rivers depends on having good recreational water quality.

The ACT’s recreational lakes and rivers sometimes have to be closed to protect human health. This is due to toxic blue-green algal blooms and enterococci bacteria. Enterococci live in the intestinal tracts of warm-blooded animals, including humans, and can enter waterways in faecal waste. People who ingest this bacteria or the toxins from blue-green algal blooms can get sick. Waterways end up with this kind of pollution mainly due to run-off from urban areas and farms. Climate change is contributing to poor recreational water quality in the ACT through hotter days, drier conditions, and severe storms. These conditions increase the likelihood of algal blooms and high levels of enterococci bacteria.

This graph shows the proportion of the recreational season that Canberra lakes were closed to recreational activities from 2015–16 to 2022–23. Lake Tuggeranong is often closed during the recreational season and Lake Ginninderra also has significant closures. Lake Burley Griffin has the fewest closures in most years due to better water quality.

Data sourced from: Environment, Planning and Sustainable Development Directorate and the National Capital Authority.

The ACT needs more effective ways to prevent polluted run-off and to improve recreational water quality so that people can enjoy our lakes and rivers. This is particularly the case for Lake Tuggeranong which frequently closes for most of the recreational swim season due to severe blue-green algal blooms and high levels of bacteria.

An enormous blue-green algae bloom on Lake Tuggeranong. Source: Alice Tschierschke.

Water resources

The Canberra community relies on water to drink, wash, cook with, and use around our homes and gardens. Most of the water we use in the ACT comes from four drinking water reservoirs. We need to use water sustainably at all times so that we have enough water stored for times of drought.

Wet times, dry times

The ACT’s water resources are highly variable from year to year. Rainfall, temperature and evaporation all affect water availability. There can be years of dry conditions, followed by wet years that replenish water storages and river systems.

Look at the graph below and compare the difference between drought periods (like 2017–18 to 2019–20) with wetter periods (like 2020–21 to 2022–23). This enormous variation shows how vital it is for us to use water sustainably, even during high rainfall periods, to ensure good resources during dry times.

This graph shows how much water flowed into the ACT’s four water storage reservoirs between 2001–02 to 2022–23. For most years, inflows were below the long-term average. The total inflows during 2018–19 was the lowest since records began in 1912, and nearly 90% below the long-term average. The wetter years from 2020–21 to 2022–23 provided inflows that were more than two and a half times above the long-term average.

Data sourced from: Icon Water.

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