Water – Background Information

Water quality can be affected by pollutants originating from urban, industrial, agricultural and mining activities, waste disposal, contaminated land, wastewater, nutrients, chemicals and stormwater runoff.

The effects of contamination depend on the pollutant, its concentration and persistence, the characteristics of the receiving waterbody and the environmental values being protected. Monitoring and assessment should therefore use appropriate water-quality objectives rather than applying a single water-quality threshold to every river, wetland or estuary. The Australian and New Zealand Guidelines for Fresh and Marine Water Quality provide the national framework for assessing and managing water quality.

Public drinking water source areas are protected through designated boundaries, priority areas, protection zones, land-use planning and drinking-water source protection reports. DWER maintains current mapping of these areas.

Known and suspected contaminated sites in Western Australia are regulated under the Contaminated Sites Act 2003 and Contaminated Sites Regulations 2006.

Climate change is altering the water cycle across south-west Western Australia. Declining rainfall has reduced streamflow and groundwater recharge, and more rainfall is now required in many systems to produce the levels of recharge and runoff experienced historically.

Water abstraction can add to these pressures where extraction occurs from groundwater or surface-water systems already affected by declining recharge or streamflow. Water allocation planning therefore considers water use together with environmental requirements and uses allocation limits, licensing rules and monitoring to protect the long-term sustainability of resources.

These pressures are already evident within the NAR. DWER’s 2024 evaluation of the Gingin allocation plans identified ongoing risks associated with declining groundwater levels and streamflow, while its updated Mid West water-supply assessment found that water availability has declined since 2015 and demand for many of the region’s best-quality and most accessible resources is increasing.

Water-resource management in Western Australia continues to operate under six separate water-resource management Acts. Earlier plans to consolidate these laws through a new Water Reform Bill were discontinued by the WA Government in December 2023.

Erosion occurs when soil and other material are detached and transported by water or wind. Along waterways, erosion can be intensified where riparian vegetation is cleared or degraded, banks are disturbed by livestock or vehicles, drainage patterns are altered or high flows destabilise exposed banks.

Sediment entering rivers, wetlands and estuaries can alter channel form, fill pools, reduce habitat complexity and increase turbidity. Fine suspended sediment reduces light penetration and can affect aquatic plants and animals. Sediment can also transport nutrients and other contaminants through a catchment.

Management could focus on preventing erosion at its source and restoring the ability of catchments and riparian zones to slow and filter runoff. Actions can include retaining groundcover, managing surface drainage, fencing sensitive foreshore areas, revegetating waterways, stabilising actively eroding banks and using appropriately designed engineering measures where natural regeneration alone is insufficient.

Eutrophication is the excessive enrichment of water with nutrients, particularly nitrogen and phosphorus. Nutrients can enter waterways and wetlands from fertilisers, livestock waste, wastewater, septic systems, soil erosion and urban runoff.

Excessive nutrient concentrations can stimulate algal growth. When algae and other organic material decompose, oxygen levels may fall, potentially affecting fish and other aquatic organisms. Some algal blooms can also reduce recreational, aesthetic and ecological values.

Agricultural catchments within the NAR can be vulnerable to nutrient movement where fertilisers or animal wastes are mobilised in runoff or leach to groundwater. Management approaches include matching fertiliser applications to crop and soil requirements, maintaining vegetation and groundcover, managing livestock access to waterways, protecting riparian vegetation and monitoring water quality to identify emerging problems.

Water-quality condition and nutrient trends should be assessed from contemporary monitoring data rather than assuming that historical observations of individual wetlands or waterways remain representative of present conditions. The Australian and New Zealand Guidelines for Fresh and Marine Water Quality provide the national framework for interpreting monitoring results.

Flooding is a natural part of river and wetland systems. It occurs when rainfall and runoff exceed the capacity of waterways, wetlands, drainage systems or floodplains. Flooding can replenish wetlands, connect aquatic habitats, redistribute sediments and nutrients and support important ecological processes, but it can also create significant risks to people, property, agriculture and infrastructure.

Flood risk varies considerably across the NAR and can be increased where development occupies natural floodplains or drainage paths, waterways are modified, vegetation is removed or drainage systems concentrate runoff.

DWER maintains floodplain mapping for a number of locations in the region, including mapped flood information for the Chapman and Greenough river systems. Current flood datasets should be consulted when assessing development or infrastructure proposals.

Western Australia’s State Planning Policy 2.9 – Water, which became operational on 18 December 2025, requires water-related considerations to be incorporated into planning and development, including management of flood risk, water quality, water quantity and water-dependent ecosystems. It replaced the former State Planning Policy 2.9 – Water Resources.

Climate change adds complexity to flood planning. Although rainfall is declining overall across Western Australia, the intensity of heavy rainfall events is expected to increase, meaning periods of water scarcity and damaging flood events can occur within the same changing climate.

Riparian vegetation is the vegetation growing beside rivers, streams, wetlands and other waterways. Healthy riparian zones stabilise banks, filter runoff, trap sediment and nutrients, shade waterways, contribute woody debris and organic matter and provide habitat and ecological connections through the landscape.  In agricultural and developed landscapes, riparian vegetation can be degraded by clearing, grazing, weeds, feral animals, altered fire regimes, erosion, salinity, changed hydrology and recreational or development pressures.

Protecting existing vegetation is generally preferable to attempting to recreate it after it has been lost. Management can include fencing waterways to manage livestock access, controlling weeds and feral animals, retaining native vegetation and large woody debris where appropriate, revegetating degraded areas with locally appropriate native species and stabilising actively eroding banks.

Foreshore and waterway assessments undertaken in parts of the NAR remain useful historical baseline information, but their age should be made clear where they are used. Site condition should be reassessed before historical condition ratings are treated as representing current conditions.

Dryland salinity remains a major form of land degradation in Western Australia’s agricultural areas. Large-scale replacement of perennial native vegetation with annual agricultural systems changed catchment water balances, increasing groundwater recharge in many landscapes. Rising groundwater can mobilise salts naturally stored in soils and regolith and bring them into the root zone, waterways, wetlands and valley floors.

Salinity can reduce agricultural productivity, alter vegetation communities, affect freshwater ecosystems, damage infrastructure and contribute to the degradation of waterways and wetlands. Waterlogging often occurs in association with shallow saline groundwater.

Groundwater responses vary across the agricultural region. In some landscapes groundwater is still rising, while in others changing rainfall and recharge patterns are altering historical trends. For this reason, older regional predictions of the future extent of salinity should not automatically be presented as current measurements.

Management depends on landscape position, groundwater processes, soil characteristics and land use and can include maintaining or increasing perennial vegetation, managing surface water, establishing salt-tolerant vegetation, protecting remnant vegetation and wetlands, and using engineering approaches where appropriate. DPIRD recommends that salinity management be undertaken as part of whole-farm and, where possible, whole-catchment water management.

Current soil, hydrology, groundwater and salinity mapping can be explored through DPIRD’s NRInfo system.