Water

Introduction

This section provides an assessment of aquatic ecosystem health, river flows and water quality in the ACT. The following indicators are assessed:

• W1: Aquatic ecosystem health
• W2: River flows
• W3: Water quality
• W4: Recreational water quality

For background information on water in the ACT see Background: Water. 

Threatened aquatic biodiversity and ecosystems are discussed in Biodiversity. Water resources and consumption are discussed in Human Settlements.

The Orroral Valley bushfire had severe impacts on the ACT’s aquatic ecosystems, including significantly degraded water quality, mortality of aquatic species and the loss of riparian vegetation. These impacts are discussed in 4. Bushfires in the ACT and should be considered in conjunction with the assessments of ACT waters presented in this section.

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.

Key findings

Key actions

That the ACT Government: 

Indicator assessments

Data summaries

General

• The Orroral Valley bushfire had severe impacts on the ACT’s aquatic ecosystems, including significantly degraded water quality, mortality of aquatic species and the loss of riparian vegetation.
• The reporting period saw extremes in weather conditions across the ACT, from the hot and dry conditions in 2019 and early 2020, to the very wet conditions from mid-2020 to 2022. These extremes have impacted on the ACT’s aquatic ecosystems and biodiversity.

Aquatic ecosystem health — Catchment Health Indicator Program

This is the second ACT State of the Environment Report to use data from the Catchment Health Indicator Program. The program assessed 71 reaches in the Ginninderra, Molonglo and Southern ACT catchments. Main findings for the 2019 to 2022 period (averaged scores) are below.

• 41% of the 71 reaches assessed were in good condition across the three catchments, and 52% were in fair condition. Four reaches were found to be in excellent condition and only one was assessed as poor.
• The 2019 to 2022 period had slightly improved overall aquatic ecosystem condition scores compared to the 2015 to 2018 period with a higher percentage of reaches in good to excellent condition (47% compared to 42%) and a lower percentage of reaches in fair to poor condition (53% compared to 58%). The small difference between the two periods is likely related to the increased rainfall and waterway flows over the 2020 to 2022 period.
• The main pressures on aquatic ecosystem condition in the ACT are land use impacts, modified river flows and climate change.
• The presence of some good condition reaches in urban areas shows that healthy aquatic ecosystems can be supported with effective management and water sensitive urban design.

Macroinvertebrate condition — Catchment Health Indicator Program

• 37% of the 71 reaches assessed were found to have good to excellent macroinvertebrate condition, 17% were found to be in poor to degraded condition, with 46% classed as fair.
• The Southern ACT and Molonglo catchments had the most reaches with healthy macroinvertebrate communities. Only one reach in the Ginninderra catchment had good macroinvertebrate condition.
• The 2019 to 2022 period saw improved macroinvertebrate condition scores compared to the 2015 to 2018 period with a higher percentage of reaches in good to excellent condition (36% compared to 25%) and a lower percentage of reaches in fair to poor condition (61% compared to 72%). The difference between the two periods is likely in response to the increased rainfall and waterway flows over the 2020 to 2022 period.

Riparian condition — Catchment Health Indicator Program

• Riparian condition scores are the worst of all the CHIP assessment components (macroinvertebrates, riparian and water quality).
• Of the 68 reaches assessed, over half (53%) were assessed as having poor to degraded riparian condition. Only 13% of reaches were assessed as having good to excellent riparian condition and 34% were found to be in fair condition.
• The Ginninderra catchment had no reaches with good riparian condition.
• The 2019 to 2022 period saw a further decline in riparian condition compared to the 2015 to 2018 period with a higher percentage of reaches in poor to degraded condition (53% compared to 48%). Changes may reflect the stress on riparian vegetation caused by the drought period prior to 2020.
• Urban and rural areas generally had fair to degraded riparian condition due to vegetation clearing. However, there were also some fair and poor reaches in conservation and protected areas.
• The replanting of native species in cleared riparian zones and the removal of weed species would greatly improve aquatic health and the amenity of aquatic ecosystems for the ACT community.

Native fish

• Native fish in the Cotter River have been significantly impacted by the 2019 drought and especially by the 2020 bushfires. These impacts are greatest upstream of Corin Dam where native fish abundance and biomass has decreased since 2019. In 2023, native species accounted for just 17% of the total fish abundance and 7% of the total fish biomass above Corin Dam.
• A combination of sediment and ash from the burnt catchment and high flows from above average rainfall since 2020 have decreased the abundance of Two-spined Blackfish (Gadopsis bispinosus) above Corin Dam to the lowest numbers since surveying began in 2000.
• The population of the alien fish Rainbow Trout has increased since the fire and has dominated fish abundance and biomass in the Cotter River above Corin Dam from 2021.
• Fish surveys in the Murrumbidgee River from 2011 to 2023 show that native fish account for around just 20% to 35% of total fish abundance with alien species (mainly European Carp) accounting for the majority of fish in the river. The biomass of native fish was similar, accounting for between 20% and 40% of total fish biomass.
• There were increased numbers and size classes for Golden Perch (Macquaria ambigua) which is benefited by high flows that increase regional connectivity.
• Although alien fish abundance and biomass is higher in the Murrumbidgee River compared to the Cotter River, results for both rivers demonstrate that alien species can dominate fish populations and impact on native fish when river systems are disturbed or degraded by pressures such as poor water quality and regulated flows.
• The presence of Murray Cod and Golden Perch in Canberra’s urban lakes and ponds is dependent on stocking. Between 2015 and 2023, nearly 222,000 Golden Perch and 230,000 Murray Cod were stocked to Canberra’s lakes and larger ponds.

River flows

• The ACT’s annual river flows are highly variable, characterised by generally dry conditions punctuated by wet years which replenish water storages and river systems.
• The ACT’s highly variable weather conditions meant that the Murrumbidgee, Molonglo, Cotter and Paddys rivers all experienced flows well below the long-term average from 2017 to 2019, and flows significantly above the long-term average from 2021 to 2022.
• For the Murrumbidgee River, flows were between three times to nearly five times higher than the long–term average in 2021 and 2022.
• Annual river flows were lowest in 2019 with the Paddys River flows just 5% of the long-term average, the Molonglo River 8%, the Murrumbidgee River at Lobbs Hole 13%, the Murrumbidgee River at Halls Crossing 16%, and the Cotter River 17%. These extremely low flows impacted on aquatic ecosystem health as well as the amenity of the ACT’s waterways.
• In 2019, cease-to-flow periods occurred for the Murrumbidgee River at Lobbs Hole, the Cotter River, the Paddys River, and the Molonglo River.
• Flows in the Murrumbidgee River are significantly impacted by the Tantangra Dam in NSW which releases less than 10% of the waters that flow into the dam.
• Over the 2015 to 2022 period, annual discharges for the Murrumbidgee River leaving the ACT were much higher than those upstream of the region.
• Over the reporting period, annual flows downstream of all ACT water supply reservoirs were greater than the environmental flow requirement. Environmental flow requirements were met despite the significantly reduced rainfall and river flows from in 2019 and early 2020.

Water quality — Catchment Health Indicator Program

Main findings for the 2019 to 2022 period (averaged scores) include:

• Water quality was found to be excellent for 41% of the 71 reaches assessed and good for 55%, with only three reaches assessed as fair condition.
• The 2019 to 2022 period saw improved water quality scores with a higher percentage of reaches in excellent condition (41% compared to 35% from 2015 to 2018). This may reflect the increased waterway flows over the 2020 to 2022 period.
• Despite the added pressures imposed by urban and rural land uses, water quality was still good in these areas, with some reaches attaining excellent condition ratings. These assessments demonstrate the effectiveness of water quality management in some urban areas, particularly as a result of constructed wetlands and other water sensitive urban design approaches.
• Periods of significantly higher nitrogen concentrations were found in the Murrumbidgee River downstream of the Lower Molonglo Water Quality Control Centre (LMWQCC), particularly when the LMWQCC discharge contributes a higher proportion of the total river flows during drought conditions.

Water quality in the ACT’s urban waterways

• Of the water quality variables monitored in the ACT, increased turbidity and nutrients from urban runoff are the main urban water quality issues impacting on aquatic health and recreational closures.

Lake Tuggeranong

• Lake Tuggeranong has regularly suffered from cyanobacterial blooms and high levels of faecal contamination. These are often accompanied by odours and highly turbid water, reducing the recreational and aesthetic value of the lake and surrounds.
• Nutrient concentrations in Lake Tuggeranong were regularly above the acceptable levels for urban lakes. Nitrogen levels are particularly high with over 80% of water samples above the acceptable range for most years.
• Lake Tuggeranong is not consistently reducing water quality impacts on downstream waters, with periods of higher phosphorus and nitrogen concentrations within and downstream of the lake compared to upstream of the lake.

Lake Ginninderra

• Current water quality issues in Lake Ginninderra are confined to rare cyanobacterial blooms and regular high enterococci concentrations, with all other water quality parameters typically within the acceptable range.
• Lake Ginninderra does not appear to be effectively mitigating the effects of urbanisation for the downstream waters with increased nutrient levels found downstream of the lake in some years.

Lake Burley Griffin

• The main pressures on the Lake Burley Griffin’s water quality and aquatic health are pollutants from the Molonglo River, discharges from the Queanbeyan Sewage Treatment Plant and pollutants from the ACT’s urban runoff.
• Lake Burley Griffin was found to be effectively mitigating pollutants, especially nitrogen, and protecting the waters downstream of the lake in most years.

Urban rivers

• Nitrogen concentrations are regularly outside of the acceptable range for the upper and lower reaches of the Molonglo River.
• Turbidity levels were regularly outside of the acceptable range for both the upper and lower Molonglo River, particularly in wetter years. Since 2019, turbidity in the lower Molonglo River has increased notably most likely due to sediment runoff caused by urban development in the Molonglo Valley.
• Turbidity issues in the lower Molonglo River suggest that sediment contributions from urban development are negating the water quality benefits provided by Lake Burley Griffin and are impacting on the water quality of the Murrumbidgee River.
• Tuggeranong Creek has high nitrogen and turbidity levels which are also a concern for the ecosystem health of the downstream Murrumbidgee River. Turbidity is also the main cause of the poor recreation and aesthetic values associated with the creek.
• Turbidity and nitrogen levels in Ginninderra Creek were also consistently outside the acceptable range.
• Concentrations of total phosphorus, nitrogen, turbidity and dissolved oxygen were consistently outside the acceptable range in Sullivans Creek with some very high concentrations recorded.
• Periods of high levels of nutrients and turbidity in Sullivans Creek impact on the water quality and amenity of Lake Burley Griffin, particularly during times of high rainfall.

Water quality entering and leaving the ACT

• Except for turbidity and electrical conductivity, water quality in the Murrumbidgee River is comparable upstream and downstream of the ACT.
• In the high rainfall years of 2020 to 2022, the number of turbidity exceedances significantly increased and were higher downstream of the ACT. This shows that the ACT contributes additional sediment and other particles that cause turbidity into the Murrumbidgee River via Canberra’s urban waterways.
• In 2020, turbidity levels downstream of the ACT experienced guideline exceedances for 85% of the days monitored and increased to 100% in 2021. This was caused by both increased rainfall runoff and extreme levels of ash and sediment from the 2020 Orroral Valley bushfire.
• Canberra’s urban lakes mitigate the downstream levels of turbidity in most years, reducing downstream impacts in the Murrumbidgee River. However, new land developments in the ACT’s western edge have no large lake to reduce potential downstream impacts. This may mean that the ACT will have a greater impact on the Murrumbidgee River in the future.

Recreational water quality 2015–16 to 2022–23

• The 2022–23 recreational season had the highest total closures across the ACT since 2015–16.
• Lake Tuggeranong has by far the poorest recreational water quality with around 60% or higher of the recreational season closed in most years.
• In 2022–23, Lake Tuggeranong was closed for nearly 80% of the season, the highest closures since 2015–16, mostly caused by high concentrations of cyanobacteria.
• The frequent recreational closures in Lake Tuggeranong clearly demonstrate a failure to meet the community’s recreational and aesthetic expectations for the lake.
• Recreational closures for Lake Ginninderra occur for around 20% or more of each season. The highest number of closures was in 2022–23 when the lake was closed for nearly 60% of the recreational season.
• High enterococci concentrations have been responsible for most of Lake Ginninderra’s recreational season closures, occurring in every season since 2015–16. This contrasts with recreational closures for Lake Tuggeranong and Lake Burley Griffin which experience more frequent periods of high cyanobacteria concentrations.
• Lake Burley Griffin generally has the fewest recreational closures. Prior to 2020–21, it was generally open for around 80% to over 90% of the recreation season. From 2020–21 to 2022–23, the lake was closed to primary contact for at least 25% of the recreational season, with 2020–21 closed for more than 30% of the season, the highest recreational closures since 2011–12.
• All of the monitored river recreation areas for the Murrumbidgee, Cotter and Paddys rivers experienced closures in every recreational season because of high enterococci concentrations.
• The Paddys River had the highest number of closures from 2015–16 to 2022–23 with five seasons having around 50% or higher of the recreational season closed. Only one season had less than 30% of the recreational season closed.

Management of Water in the ACT

Context

The ACT’s waterways are expected to be increasingly subject to extreme and variable climatic conditions in coming years. Within this context, management of waterways is especially challenging. In particular, balancing anthropocentric outcomes such as flood protection and domestic water supply with providing habitat and high-quality water for native species will be increasingly difficult.

Refer also to Human Settlements for information about water consumption and supply.

Policy framework

The Water Resources Act 2007 aims to ensure that management and use of the water resources of the Territory sustain the physical, economic and social wellbeing of the people of the ACT while protecting the ecosystems that depend on those resources. The ACT Water Strategy 2014–44:  Striking the Balance provides long term strategic guidance to manage the Territory’s water resources. It is intended to guide the development, integration and implementation of activities undertaken by ACT Government and its partners, developers, the ACT community, natural resource management groups and other stakeholders involved in planning, water management and water use. Four-year implementation plans are developed to provide detail about how the ACT Water Strategy 2014–2044 is put into practice, with the most recent of these plans ending this year. 

The Aquatic and Riparian Conservation Strategy and Action Plans 2018 provides guidance on the conservation of aquatic and riparian areas and component species. They include recommendations to address a range of key threats to aquatic and riparian species and ecosystems as well as action plans for threatened aquatic species. The management and enhancement strategies identified within it aim to increase the resilience of aquatic and riparian areas to threats such as climate change. However, urban lakes, ponds and waterways are not specifically covered in the strategy.

Aquatic habitat in the ACT’s rivers is also supported by the Environmental Flow Guidelines 2019 (No 2), an instrument under the Water Resources Act 2007 that sets out the flow requirements (quantity and timing) needed to maintain freshwater ecosystems. Among other things, the guidelines seek to maintain the minimum volume of water that a river needs to support the fish, plants, insects and protect water quality. The volume of this base flow is determined for each month for each stretch of stream or river, taking into account environmental conditions. Larger ‘flood’ flows are also built into management guidelines to mimic natural periods of higher flow and reduce the likelihood of sediment build-up in waterways.

During this reporting period, work has commenced on developing Aboriginal Water Assessments in collaboration with Ngunnawal Traditional Custodians. These assessments offer a way for Ngunnawal cultural and ecological knowledge to be incorporated into the management of waterways in the ACT region.

The Nature Conservation Act 2014, Environment Protection Act 1997 and Planning Act 2023 also contain elements which govern the management of water and aquatic habitats in the ACT.

Policy effectiveness

The State of the Lakes and Waterways in the ACT report published by the Office of the Commissioner for Sustainability and the Environment in 2022 discusses urban water management in the ACT in detail. This report found arrangements for urban water management in the ACT are complicated, with many different agencies playing a role in water management. This can lead to undesirable outcomes as responsibilities and communications between different entities are not always clear. The establishment in 2022 of the Office of Water to coordinate policy and management approach is a positive step but its work so far is still confined to the Environment, Planning and Sustainable Development Directorate, which has limited responsibility for water management within the urban area. An overarching framework for water management in the ACT which also includes Transport Canberra and City Services, the Environment Protection Authority and ACT Health is lacking.

The State of the Lakes and Waterways in the ACT report made 12 recommendations regarding water management in the ACT, of which 11 were agreed to by the ACT Government. Implementation of the recommendations is still at an early stage.

Since the publication of the State of the Lakes and Waterways in the ACT, a number of Territory Plan General Codes — frameworks which guided the sustainable use of water in the ACT — have ceased to have effect under the new Territory Plan. Different mechanisms will be in place under the new Territory Plan to guide water management in urban areas and it remains to be seen what effect these will have on Canberra’s approach to Water Sensitive Urban Design.

Greenfield developments continue to be a major contributor to sediment and nutrients entering the Molonglo and Murrumbidgee rivers. There is evidence from the recent past that erosion and sediment control measures put in place during the land clearing and construction phases have not always been adequate to prevent high sediment loads entering the rivers. It is essential to address this for future developments planned within river catchments.

Current knowledge about the detailed ecology of many native aquatic species is incomplete and this makes it challenging to know which targeted management interventions are needed. Therefore, protection of aquatic and riparian habitats through broadscale actions for water quality and habitat improvement, such as prevention of sedimentation and removal of invasive species, is likely to offer the best option for the conservation of surviving native aquatic species.