SoE 2009 > Water > 6.2 River health

6.2 River health

Prolonged drought, combined with changes to river flows, has placed most inland river systems under critical stress. As a result most inland rivers are in poor ecosystem health, whereas coastal rivers are generally in better health. Water sharing plans are being implemented for all major rivers in New South Wales to ensure a balance between human uses of water and the environment.

Historically, the environmental condition of the majority of NSW rivers has been modified, through the effects of water extraction and river regulation, vegetation clearing, catchment disturbance and declining water quality.

In the shorter term, ongoing drought conditions across much of NSW since 1997 have severely limited water availability. This has contributed to a decline in river health indicators such as macroinvertebrates and fish in many areas of the state.

The growing demand for water resources and recent climatic conditions are both major determinants of the condition of freshwater riverine systems. Areas where the flow regime has changed the most (where river regulation and water use are highest) are generally showing the greatest signs of ecosystem stress.

Greater availability of water for the environment is being addressed through water sharing plans and water and licence buyback. A wide range of programs is being implemented to restore various aspects of river health, including river flows, riparian vegetation, fish passage and fish community composition and to improve water quality and catchment management practices.

NSW indicators

Notes: Terms and symbols used above are defined in About SoE 2009 at the front of the report.

Introduction

Healthy riverine ecosystems, comprising rivers and their riparian zones, floodplains and wetlands, are vital for the maintenance of aquatic and terrestrial biodiversity. However, while aquatic ecosystems have their own intrinsic value, healthy rivers are also critical for maintaining good water quality and providing ecosystem services that support the beneficial use of water by humans and activities such as agriculture, aquaculture, fishing, recreation, tourism and swimming. Rivers play an important role in connecting aquatic ecosystems and terrestrial environments.

NSW has approximately 58,000 kilometres of rivers and major streams. These can generally be categorised as either short, high-gradient coastal streams or long, low-gradient inland rivers. The flow of these rivers is highly variable and often unpredictable. Streams and creeks may flow permanently or only intermittently after heavy rainfall and floods. About 97% of river length in NSW has been substantially modified (NLWRA 2002). Typical changes include the removal of riverine vegetation, the regulation of river flows, sedimentation from erosion of land and riverbanks, and the introduction of exotic species.

A river is in good health if it is resilient in the face of environmental change, including changes in climate, resource exploitation or other human impacts. A primary objective is to achieve a long-term balance, whereby the integrity of natural systems is preserved while providing for a range of beneficial human uses.

This section focuses on inland and coastal freshwater riverine ecosystems, including floodplains which are essential for connecting many types of freshwater wetlands and associated ecological processes to the rivers. Other ecosystem types are discussed elsewhere in this report: freshwater wetlands in Water 6.4 and estuaries in Water 6.6.

Status and trends

River health

The Sustainable Rivers Audit (SRA) has developed a methodology to assess the health of rivers in the Murray–Darling Basin based on indexes for hydrology, fish and macroinvertebrates. A set of expert rules is used to combine the three to determine an overall rating of river valley health (MDBC 2008a). Overall results for basin systems are summarised in Table 6.6 and described in greater detail below.

Table 6.6: Ecosystem health and condition assessments for NSW Murray–Darling Basin rivers, 2008

Source: MDBC 2008a

Development of a complementary assessment process for coastal rivers in NSW has now commenced (Table 6.7), but no assessment is available for the areas of NSW west of the basin.

Table 6.7: Ecosystem health and condition assessments for NSW coastal rivers, 2008

Source: DECC, DWE and DPI data 2008

Notes: Hydrological condition uses the same methodology as SRA except those marked * where only an interim assessment has been made.
Fish condition uses the same methodology as SRA with some minor adjustments.

Hydrology

River flow influences virtually every facet of river ecosystem health and is therefore indicative of river condition. The SRA hydrology condition index consists of five indicators reflecting the relative ecological importance of high and low flow events, changes in flow variability and seasonality, and annual flow volume. All are assessed by comparing flows to reference condition for each river.

The SRA hydrology indicators use modelled data based on flow variability over the longer term (110 years of recording). They represent the overall effects of water resource development on historical flow patterns, or the naturalness of the flow regime. However, these results are less indicative of shorter term variability or current flows, so do not reflect the drought conditions that prevail in much of the Murray–Darling Basin at present.

Inland rivers: The SRA found that most sites in the Murray–Darling Basin were in moderate to good hydrological condition (see Table 6.6). Those sites that fell short of reference condition were mostly in the main channels of some of the major regulated rivers – the Murrumbidgee, Macquarie, Lachlan and Condamine–Culgoa – as well as the unregulated Darling, with most sites rated as poor in the lowland zones of these major rivers. The Paroo River was rated as being in good hydrological condition throughout as its flow regime is little changed from natural (MDBC 2008a).

Coastal rivers: Hydrology was modelled similarly for those coastal rivers of NSW where sufficient data was available. However in the majority of streams this was not the case and an interim assessment was made based on the degree to which annual flows in a dry year are affected by extraction. The coastal rivers of NSW were mostly rated as being in good condition (see Table 6.7). Only the Macquarie–Tuggerah Lakes and Snowy were rated as being in poor condition, reflecting major changes to flow regimes in these rivers. The Hawkesbury and Georges rivers were rated moderate, reflecting the impacts of urban development in their systems.

Fish

The SRA fish community index (MDBC 2003a) describes the condition of fish communities using indicators for fish numbers, biomass and community composition.

Inland rivers: Overall, the fish condition index scores indicate that condition was very poor in most valleys (Table 6.6). Communities in the north-west of NSW were generally in better condition than those in the south-west. Many native fish species expected to occur in some valleys were not recorded at all. Alien fish species rivalled or out-numbered native fish species in the Macquarie, Gwydir and Murrumbidgee valleys but high proportions of native fish biomass were recorded for the Paroo (78%), Darling (62%) and Border Rivers (60%) valleys. The Darling River had the greatest combined biomass of native and alien fish (16.8 kilograms per site) and the greatest native fish biomass (10 kg/site) (MDBC 2008a).

Coastal rivers: Limited data was available for the coastal rivers of NSW, with assessment possible for 15 of the 22 rivers (Table 6.7). Where data was available, the majority of rivers were rated as moderate to poor. Five waterways – the Manning River, Macquarie–Tuggerah Lakes, Georges River, Clyde River–Jervis Bay and NSW stretch of the Genoa River – were given a moderate rating for the fish condition index while the Snowy and Shoalhaven rivers were very poor.

Macroinvertebrates

The SRA macroinvertebrate index (MDBC 2003b) describes the condition of macroinvertebrate communities in rivers. The index integrates indicators for observed macroinvertebrate families (compared with reference conditions) and sensitivity to disturbance. For coastal rivers, macroinvertebrate community composition was evaluated using a related but slightly different methodology called AUSRIVAS (Simpson & Norris 2000).

Inland rivers: Overall, there were distinct differences between the condition of macroinvertebrate communities in the southern and northern valleys, and between upland and lowland zones of the Murray–Darling Basin (MDBC 2008a). Communities in the Castlereagh and Central and Lower Murray showed lower diversity (fewer families) than expected under reference condition while those in the Paroo, Border and Upper Murray rivers were in the best (moderate) condition (see Table 6.6). Most other rivers received ratings of poor or worse.

Coastal rivers: Macroinvertebrate communities in the majority of coastal river catchments were in fair to good condition (see Table 6.7). The middle sections of the Shoalhaven, Tuross, Moruya and Clyde rivers and upland sections of the Brunswick River and the Tuggerah Lakes catchment were in excellent condition. Only the coastal fringes and floodplains of the Sydney region and Brunswick River rated poorly. The coastal fringes of the Tweed, Richmond, Tuggerah Lakes (Central Coast streams) and Bega catchments also showed signs of disturbance.

Ecosystem health

Map 6.1 shows the overall SRA rating of ecosystem health, by river valley, for the inland rivers of the Murray–Darling Basin only. The overall assessment of river health is based on a combined assessment of the hydrology, fish and macroinvertebrate indexes shown in Table 6.6. Overall, the Paroo was the only river found to be in good ecosystem health, while the Border Rivers were in moderate health. Most other rivers received river health ratings of poor or worse.

Map 6.1: SRA assessment of river health in the Murray–Darling Basin, 2008

Due to the relatively recent commencement of broadscale coastal monitoring, it is not yet possible to make an overall assessment of ecosystem health for coastal rivers.

Threatened species

Declining biodiversity and the number of threatened species in Australia is of serious environmental concern. While many mammals, birds and other terrestrial species are threatened, aquatic animals are also under threat.

In NSW seven of the 25 native freshwater fish species found in lowland rivers are listed as threatened with extinction under the Fisheries Management Act 1994. This is almost double the number reported in NSW State of the Environment 2006 (DEC 2006). Three freshwater invertebrates have also been listed as endangered species under the Act and the status of many other species is of concern for conservation purposes.

Three aquatic ecological communities have been listed as endangered under the Fisheries Management Act:

• the Lowland Murray River ecological community
• the Lowland Darling River ecological community
• the Lowland Lachlan River ecological community.

Water quality

Salinity

Geology, climate, groundwater interactions and land-use practices all affect the level of salinity in NSW streams. High salt concentrations can degrade freshwater aquatic ecosystems and irrigation water with high salt loads can increase soil salinity.

Electrical conductivity is a measure of the amount of salt in water. Continuous monitoring of electrical conductivity has been established at 10 end-of-valley sites in the inland catchments of NSW. Table 6.8 shows mean daily salinity levels for the current and two previous SoE reporting periods and the maximum salinity level recorded for the whole period of record. This shows that the mean daily salinity levels are well below the World Health Organization desirable upper limit for drinking water of 800 electrical conductivity units (EC). However the maximum spot readings in Table 6.8 indicate that the limits for drinking water are exceeded in most systems for short periods.

Compared with 2000–03 and 2003–06, the current SoE period shows an overall decrease in mean daily electrical conductivity in streams. It appears that this may be due to the ongoing drought, which continues to limit the mobilisation of salts into streams, affecting the salinity levels recorded.

Table 6.8: Electrical conductivity in selected NSW rivers

Source: DECCW data 2009

Notes: '2003–06 mean' is based on data only available to March 2006.
'2006–09 mean' is based on data available from July 2005 to June 2008.
'Maximum spot readings' (not means) cover the entire period of record.
* End-of-valley site
** Incomplete record for reporting period

Nutrients

Nutrients, especially nitrogen and phosphorus, can have a significant effect on water quality when present in excess of ecosystem needs. The current guidelines for water quality (ANZECC & ARMCANZ 2000), along with NSW River Flow Objectives, provide trigger values for water quality parameters designed to protect potential uses of water. Trigger values are conservative and exceedences of them indicates the need to investigate possible causes, but does not necessarily signify poor river health.

Map 6.2 shows the proportion of phosphorus samples from streams across NSW that exceed ANZECC trigger values. The figures reveal that phosphorus is regularly above trigger values (>50% of the time) at most sites in the upper and middle reaches of the major inland rivers of NSW. Exceedences were recorded less frequently in coastal rivers.

Phosphorus levels were generally lower in the South Coast streams and along the main channel of the Murrumbidgee River. The northern inland catchments – the Namoi, Darling, Macquarie and Gwydir – showed the highest levels of exceedences of trigger values. Some sites in the north-west of NSW exceeded the trigger values by an order of magnitude, having median total phosphorus levels of 0.5 milligrams per litre compared with a trigger value of 0.05 mg/L. In these areas nearly all samples exceeded the guidelines.

High phosphorus levels are considered to be the most significant risk factor for eutrophication in fresh water, in conjunction with other factors such as nitrogen, light conditions and water temperature (Davis & Koop 2006).

Map 6.2: Exceedences of ANZECC trigger levels for total phosphorus in streams and rivers across NSW, 2005–08

Algal blooms

Most of the problematic freshwater algal blooms that occur sporadically in NSW are caused by blue-green algae (also known as 'cyanobacteria') and some of these produce toxins that are harmful to humans, livestock and aquatic fauna. However, non-toxic blooms can also have significant impacts on the health of aquatic ecosystems by depleting dissolved oxygen, changing pH, reducing light penetration and smothering habitat.

A number of environmental factors may interact to increase the risk of algal blooms developing in freshwater systems. These include warm water temperatures, elevated nutrient concentrations and low river flows. Drought exacerbates the problem of algal blooms by producing warm, still waters, which are ideal conditions for algal growth.

Pressures

Water extraction and altered flow regimes

Beyond the continuing drought, water availability to the environment has been reduced in most inland river and wetland systems through water extraction and flow regulation. Altered flow regimes also affect the seasonality and variability of flows, dampening both the peaks and troughs in water levels. This has an impact on critical ecological processes that trigger breeding cues for bird and fish species, and has been a significant factor in the loss of biodiversity and the decline of aquatic ecosystems over the longer term.

'Alteration to the natural flow regimes of rivers and streams and their floodplains and wetlands' has been listed as a Key Threatening Process (KTP) under the Threatened Species Conservation Act 1995. A related process, 'the installation and operation of in-stream structures and other mechanisms that alter natural flow regimes of rivers and streams' is also a KTP but under the Fisheries Management Act 1994.

The alteration to natural flow regimes encompasses a range of changes or disturbances, including to the frequency, duration, magnitude, timing and variability of flow events, altered surface water levels and seasonality of flows, and changes to the rate of rise or fall of water levels. Water resource development, while necessary to provide resource security and access, is the main cause of alterations to natural flows through the building of dams and weirs, diversion or extraction of in-stream flows and the alteration of flows on floodplains by levees and other structures.

Extreme drought

In the shorter term, prolonged drought can place severe stress on aquatic ecosystems. Most inland aquatic ecosystems are adapted to drought conditions and recover quickly when flows are resumed. Many species actually depend on variability in flows to complete critical stages in their life cycles. However, when the cumulative effects of drought conditions and water extraction continue over an extended period, critical thresholds in life cycles may be exceeded, placing prospects for recovery at risk. For many regions of NSW the present drought conditions are among the worst ever recorded and prospects for recovery of some species and ecosystems are now under increasing threat.

Due to long-term changes in river condition, native fish populations are now much reduced and less resilient to change, placing many species under additional stress during the ongoing drought conditions. For example, the drying of a stream near Holbrook in southern NSW resulted in the rescue and holding in captivity of its entire population of southern pygmy perch, while Macquarie perch in the Queanbeyan River have not recruited since 2001 due to extremely low flow conditions (MDBC 2007).

Floodplain fragmentation and harvesting

Floodplains are the areas of land that would naturally receive waters during floods. Historic settlement on them has changed natural flow patterns and the behaviour of floods. Structures that alter the course of floods include levee banks constructed to harvest water or protect property, as well as bridges, roads and railway lines. The redirection of floodwaters and a reduction in their levels of flow have a significant impact on the health of riverine and wetland ecosystems.

Floodplain harvesting is the practice of diverting, collecting or capturing floodwaters that flow across a floodplain. This has largely been conducted without management in NSW, although a draft policy on floodplain harvesting has now been released. The Murray–Darling Basin Cap, which limits the extraction of water from all NSW catchments and rivers, does not currently account for water diverted by floodplain harvesting, although extraction limits set in NSW water sharing plans include an allowance for floodplain harvesting. Private landholders own 95% of NSW floodplains and it has been estimated that half of all landholders engaged in floodplain grazing have experienced a 50% reduction in income due to reduced floodwater flows (Kingsford 2000).

Catchment disturbance

Activities in river catchments can have a significant impact on riverine ecosystems, primarily through a reduction in water quality. Agriculture, urban stormwater and effluent can introduce nutrients, pollutants, suspended sediments and other contaminants into rivers and streams.

Management of water pollution remains a significant challenge in maintaining riverine ecosystem health. While point source pollution has largely been addressed through regulatory processes, diffuse source pollution still poses a problem for water quality (DECC 2009b). There is a wide array of possible sources of diffuse pollutants, including sediments and nutrients washed into streams in runoff from urban developments or agricultural lands. The quality and quantity of water received within a catchment largely depends on the extent of vegetation cover and land management practices in the catchment – the more development, the greater the impact on riverine ecosystems.

Riparian vegetation provides habitat and food for aquatic communities so its disturbance is of particular significance for river health. Riverbank integrity is also critical because many species hide under overhanging banks. The loss or degradation of the riparian zone is commonly caused by the clearing of vegetation and trampling by stock.

Water temperature

Cold water pollution is caused by low-temperature water being released into rivers from large dams during summer. Cold water releases can prevent the natural seasonal changes in river temperature and reduce the range of temperature variation, both seasonally and diurnally, sometimes for hundreds of kilometres downstream. These variations may affect fish breeding, hatching of fish eggs (Astles et al. 2004) and ecosystem productivity.

Discharge of cold water from dams is believed to be one of the main factors behind severe decline in native warm-water fish species in the Murray–Darling Basin (Phillips 2001). Nine dams in NSW are likely to cause severe cold-water impacts: the Blowering, Burrendong, Burrinjuck, Copeton, Hume, Keepit, Khancoban, Pindari and Wyangala storages (Preece 2003).

Invasive species

Alien fish compete for food and space with native fish and frogs. They also prey on fish and frog eggs, tadpoles and juvenile fish, fundamentally altering food webs and habitats. The Sustainable Rivers Audit found that three alien species – common carp, gambusia and goldfish – were present in all inland rivers in NSW. Redfin perch, brown trout and rainbow trout were also widespread. Carp were overwhelmingly dominant, making up 87% of alien fish biomass and 58% of total fish biomass. Carp and gambusia were the dominant species in all lowland rivers in the Murray–Darling Basin (see also Biodiversity 7.4).

Climate change

According to the findings of the CSIRO Sustainable Yields Assessment (CSIRO 2008a), the impacts of climate change on environmentally beneficial flooding in most regions of the Murray–Darling Basin, especially the highly developed regions, would be smaller than the impacts already brought about by water resource development. However, when the incremental impacts of climate change are superimposed on the existing pressures of water resource development, the ecological consequences could be substantial. This is because important ecological thresholds may be crossed and the changes that result may be largely irreversible (CSIRO 2008a).

Under a median climate change scenario, impacts by 2030 are expected to include:

• extended dry periods between important flood events and reduced flood volumes for the Murray icon sites identified in The Living Murray program (CSIRO 2008a)
• a 10% increase in the interval between beneficial flood events in the Macquarie River (CSIRO 2008b)
• a 24% increase in the flood interval in the Lachlan River (CSIRO 2008c).

Responses

State Plan 2006

State Plan 2006: A new direction for NSW (NSW Government 2006) has the following target under Priority E4: 'By 2015 there is an improvement in the condition of riverine ecosystems'. A Monitoring, Evaluation and Reporting (MER) strategy is being implemented to monitor progress towards all E4 targets.

A review of State Plan 2006 commenced in August 2009 and this may adjust some of the plan's priorities and targets.

Environmental water availability

Water sharing plans are the most significant development towards addressing river health in NSW, by improving the management of river flows and water extraction practices. They are described in greater detail in Water 6.1.

Water recovery: Improving the condition of aquatic ecosystems is a high priority for NSW. The Australian and NSW Governments are recovering water through the purchase of water entitlements and infrastructure works under a number of programs, including NSW RiverBank, The Living Murray program, the Water for Rivers Project (Snowy) and the NSW Wetland Recovery Program. Further information on water recovery is available in Water 6.1.

The Living Murray program has the objective of recovering 500 GL of water for the Murray River to address declining river health. Six icon sites have been chosen as the focus of the program because of their high ecological value and cultural significance. In NSW, they include the Millewa Forest, Koondrook–Perricoota Forest, the Chowilla Floodplain and the river channel itself.

NSW Rivers Environmental Restoration Program aims to arrest the decline of the most stressed and iconic rivers and wetlands in NSW and targets important wetlands in the Macquarie Marshes and the Gwydir, Lachlan and Murrumbidgee river systems. Most of the $173 million allocated to the program is available for water purchase and the costs associated with the management and use of water licences. The remainder is to ensure the benefits of the acquired water are secured, maximised and demonstrated.

Flow management initiatives

NSW Weirs Policy: This policy was developed to halt and, where possible, reduce and remediate the environmental impacts of the over 3300 dams and weirs on NSW rivers. A central issue for water sharing plans is the degree to which any management recommendations to remove or modify weirs affects water resource availability and water sharing arrangements.

Draft Floodplain Harvesting Policy: Announcement of this draft policy in 2008 was an important step towards managing water on floodplains in NSW. The policy will bring floodplain harvesting into the statutory framework for water management for the first time. Under the policy, floodplain harvesting extractions will be licensed and limited to the allowance provided for in each water sharing plan. No further works for floodplain harvesting will be approved.

Rural floodplain management plans have been gazetted or are being prepared for 14 major rural floodplains covering about 28,510 square kilometres. The floodplains involved are associated with sections of the Namoi, Gwydir, Macquarie, Lachlan, Murrumbidgee and Murray rivers, Billabong Creek and the Liverpool Plains. An objective of the plans is to reconnect at least 60% of the area flooded in a natural one-in-five-yearly flood to the river.

Pollution strategies

NSW Diffuse Source Water Pollution Strategy: Pollution from diffuse sources accounts for the majority of pollutant loads in the state's waterways. The objective of this strategy (DECC 2009b) is to reduce diffuse source water pollution in all NSW surface and groundwaters. The strategy's primary focus is on sources of pollutants that are not currently regulated. The three main pollutants to be addressed are sediments, nutrients and pathogens, which can arise from a multitude of sources, including agricultural land uses, sealed and unsealed roads, and urban stormwater.

Cold Water Pollution Strategy: In 2004, the NSW Government adopted this strategy to manage the impacts of cold water releases from large dams through a long-term program of improvements targeted at high priority dams. It is to be conducted in five-yearly stages with implementation of Stage 1 currently under evaluation.

Fish strategies

Native Fish Strategy for the Murray–Darling Basin 2003–2013 (MDBMC 2003) has the long-term goal of rehabilitating native fish communities back to 60% of estimated pre-European fish populations by the year 2050 (MDBC 2006). It provides a framework for:

• protecting and rehabilitating fish habitat
• improving the management of in-stream structures, thus reducing barriers to fish passage and the impact of cold-water pollution
• controlling exotic fish species
• protecting threatened native fish species
• better managing fish translocation and stocking.

The construction of fishways or fish ladders to remediate the impacts of weirs and dams on the passage of fish along rivers in NSW is an important and effective strategy in improving the health of fish communities. Between 2006 and 2008, 1600 kilometres of fish passage was reinstated upstream of 16 barriers through modification to them and removal of a further 13. Changed management regimes at 55 floodgates have also improved fish passage in coastal waterways.

Future directions

Commitment to the water reform process should be maintained. Further purchases of water licences and water savings will provide a better balance between the needs of users and the environment, with more water being allocated to improving river health.

Monitoring of environmental flows will facilitate adaptive management so that environmental flows are better targeted to maximise ecological benefits.

It is likely that harvesting of water from floodplains will be regulated and the development of floodplain management plans will provide for better protection and management of important floodplain ecosystems.

While point sources of water pollution are generally well managed, there is still scope to improve the management of diffuse source pollution, primarily from agricultural runoff and urban stormwater. Stormwater harvesting developments, runoff controls and initiatives to promote revegetation and better land management practices in catchments are being implemented to improve water quality.

Acid sulfate soils have recently emerged as an issue for inland rivers. Better information is needed on their location and the conditions under which acid contamination is likely, so that the risk of acid discharge into rivers can be minimised.

Further research is desirable to determine the likely effects of climate change on aquatic ecosystem health due to changes in water availability and possible shifts in community composition due to the altered seasonality of flows.

Many native fish species have been under severe pressure during the ongoing drought. The recovery of species when more typical flows are resumed should be monitored and measures, such as restocking considered, where appropriate.