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.
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
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.
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 concentration of oxygen 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.
Condition and trends
Water quality – Catchment Health Indicator Program
The CHIP assesses water quality for each reach using the results of monthly surveys from all sites (where possible). The assessment methodology can be found in the 2018 CHIP report.Upper Murrumbidgee Waterwatch, 2018, Catchment Health Indicator Program 2018, Waterwatch, Canberra. Water quality parameters monitored are pH, electrical conductivity, turbidity, dissolved oxygen, phosphorus and nitrate. These parameters have been widely established as the best indicators of water quality while being relatively easy to measure.
Water quality was assessed for 66 reaches in the Ginninderra, Molonglo and Southern ACT catchments. Water quality was found to be excellent for 35% of reaches and good for 62%, with only 2 reaches assessed as fair condition (Figures W24 and 25). All catchments had the majority of their reaches in good to excellent condition. The Southern ACT catchment had 62% of reaches in excellent condition.
Figure W24: Average Catchment Health Indicator Program water quality score for catchment reaches, 2015 to 2018.
As with all other CHIP parameters, condition is linked to land use with the majority of excellent condition reaches on conservation and protected land. However, 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 design approaches. Water quality results may also reflect the drier conditions for most of the reporting period. Decreased rainfall reduces the occurrence of urban and rural run-off which are main contributors to water quality decline in the ACT.
Although the ACT’s water quality was generally good, nitrogen concentrations are much higher in the Murrumbidgee River downstream of the Lower Molonglo Water Quality Control Centre (LMWQCC), with concentrations second only to the Molonglo River immediately downstream of the LMWQCC (Murrumbidgee River downstream of the LMWQCC refers to those reaches downstream of the Molonglo River confluence. The Molonglo River receives discharges from the LMWQCC immediately upstream of the confluence with the Murrumbidgee River). Nitrogen concentrations (measured as nitrate) for the Murrumbidgee River downstream of the LMWQCC ranged from 4–30 mg/l in 2018, compared to around 1 mg/l upstream of the ACT, and an excellent nitrate score for the Murrumbidgee River reach upstream of the LMWQCC discharge. A nitrate concentration of greater than 2.6mg/l is considered to be degraded under Waterwatch condition thresholds.
The high nitrate concentration in the Murrumbidgee River continues downstream of the ACT, particularly during dry periods when the LMWQCC discharge contributes a higher proportion of the total river flows. More information is required on the impacts of the LMWQCC on aquatic ecosystems in the Murrumbidgee River.
Water quality entering and leaving the ACT
It is important that the quality of water leaving the ACT via the Murrumbidgee River should be comparable to that entering the region. However, a range of pressures, especially those related to land use, can degrade water quality within the ACT. The impact of the ACT on water quality is determined by comparing ACT Government monitoring results for the Murrumbidgee River at sites upstream and downstream of the ACT. In situ water quality probes measure pH, electrical conductivity, dissolved oxygen (as a percentage of saturation) and turbidity. Phosphorus and nitrogen are not assessed by these probes.
Except for turbidity, monitoring results show that all, or nearly all of water quality samples taken in the Murrumbidgee River met guideline levels over the 2015 to 2018 period. This was for sites upstream and downstream of the ACT. Turbidity guideline exceedances were high for both upstream and downstream sites in the years 2015 to 2017 (Figure W26). Exceedances in 2018 were lower than other years and are likely related to reduced rainfall and catchment run-off. The number of turbidity samples exceeding guideline levels was higher upstream of the ACT for all years except 2016.
Figure W26: Percentage of days exceeding the turbidity guideline level for the Murrumbidgee River upstream (Lobbs Hole) and downstream (Halls Crossing) of the ACT, 2015 to 2018.
Water quality results for the period 2015 to 2018 show that pH, electrical conductivity, dissolved oxygen and turbidity in the Murrumbidgee River is comparable upstream and downstream of the ACT, with turbidity slightly improving as the river moves though the region. This change suggests that sediment and other particles that cause turbidity are being deposited in the ACT, with a likely impact on ecosystem health and biodiversity. Results also show that turbidity is the main water quality issue for the Murrumbidgee River for the variables assessed. Turbidity was also reported as one of the most serious water quality issues in the ACT’s State of the Environment 2015 report.
However, results for water quality monitoring undertaken for CHIP show that the ACT is increasing nitrogen levels downstream of the LMWQCC (see the Water quality – Catchment Health Indicator Program).