State of the Environment Report 2007
Western Australia has many different types of inland waters. Flowing waters on the surface of the land are referred to as waterways and may include estuaries, rivers, streams, creeks, drains and floodplains. There are about 208 major waterways with a combined length of 25 000 kilometres (km), and 171 estuaries (Water and Rivers Commission, 2000a). Standing waters on the surface of the land are referred to as wetlands and may include lakes, swamps, damplands, sumplands, springs, soaks, karst caves and waterholes. The State has thousands of waterways and wetlands that have water on either a permanent, seasonal or intermittent basis. Groundwater is located at various depths below the land surface and interacts with many waterways and wetlands.
Inland waters and the water cycle are fundamental for sustaining life and ecological processes. They are usually considered within the context of their drainage basins, catchments and discharge zones. These systems are essential for maintaining biodiversity and regulating catchment water balances (see 'Biodiversity'). They provide economic and social benefits by providing drinking water and irrigation water supplies, supporting food production and underpinning a diverse array of recreational, spiritual, inspirational, scientific, cultural and educational values. However, these aspects will be investigated in other areas of this report (see 'Water use in settlements' and 'Water supply').
Most inland waters in WA have been significantly modified since European settlement, especially in the South West (Finlayson & Rea, 1999; Pen, 1999; National Land and Water Resources Audit, 2002). Waterways, wetlands, floodplains and catchments have been dramatically altered to allow for settlements, agriculture, water supplies and infrastructure development. The amount and rate of alteration is largely a consequence of population growth and the consumption of natural resources to support human settlements and economic productivity (see 'Fundamental pressures'). Alteration of areas from their natural state inevitably results in detrimental changes to water quantity and quality. If persistent, these problems can lead to a rapid deterioration of both aquatic and terrestrial ecology and human related beneficial uses.
Seventy-seven per cent of estuaries (i.e. 132 of 171) are in a largely unmodified state (Geoscience Australia, unpublished data).
Thirty-two per cent of major river basins (i.e. 12 of the 38 that are monitored) are in largely unmodified state (Halse, Scanlon & Cocking, 2002).
Only 17% of remaining wetlands on the Swan Coastal Plain have high conservation significance (Environmental Protection Authority, unpublished data). Information about the condition of other WA wetlands is extremely limited.
Recent analysis indicates that wetland vegetation on the Swan Coastal Plain decreased by about 1500 hectares per year between 1996 and 2004 (Environmental Protection Authority, unpublished). This equates to the loss of an area about the size of two football ovals per day.
Environmental values for Gnangara Mound, and the Swan-Canning and Peel-Harvey estuaries are formally declared in environmental protection policies under the Environmental Protection Act 1986. While environmental values have been identified informally for other inland waters, most have not been developed in collaboration with the community and have not been afforded regulatory protection under formal State environmental policy.
Estuaries are semi-enclosed coastal water bodies were salt water from the marine environment mixes with freshwater draining the land. They are well known for their high productivity. There are 171 identified estuaries across WA (Figure IW0.1), ranging from tidal-dominated in the North West (with tides up to 10 m in places) to wave-dominated in the South West. Estuary condition is assessed using factors such as catchment vegetation cover, altered water regimes, altered tidal regimes, land and estuary uses, impacts to floodplain and estuary ecology and introduced plants and animals (National Land and Water Resources Audit, 2002), Near-pristine estuaries are generally found only in remote areas (e.g. western parts of the Kimberley) and/or those with forested catchments protected by conservation reserves. Extensively modified estuaries (e.g. Swan-Canning, Peel-Harvey, Leschenault, Vasse-Wonnerup and Oyster Harbour) have catchments with large populations, significantly modified catchments and hydrology, and intensive agriculture or industrial land uses.
![Figure IW0.1: Condition of Western Australian estuaries. [Data source: Geoscience Australia; Presentation: EPA.]](/site/files/images/Figure-IW0.1_Large.jpg)
Western Australian rivers range from permanently flowing in high rainfall areas to seasonally flowing or intermittent in low rainfall areas. Rivers are the link between land and ocean, providing estuaries and floodplains with nutrients and water needed for maintaining plant and animal life. The presence of key macro-invertebrates has been used as an indicator of the condition of river ecosystems (Figure IW0.2, Halse, Scanlon & Cocking, 2002). Rivers were found to be healthier in basins that have retained most native vegetation (i.e. in conservation reserves) or where minimal development has occurred (e.g. rivers in the western Kimberley, the Pilbara and some forested parts of the South West). Modified river basins occur throughout most of the State's South West, where many rivers have been regulated and where catchments support large settlements or intensive land uses. Some modified river basins are also found in the Mid West and the Ord River where pastoralism, river damming or mining practices have modified river ecosystems. The Avon and Esperance river basins are extensively modified due to widespread land clearing for agriculture, artificial drainage, widespread salinisation, river modification to prevent flooding, and the general loss of river structure, function and ecology.
![Figure IW0.2: Condition of major Western Australian rivers, by river basin. [Data source: Department of Environment and Heritage [ver. 2001]; Analysis: EPA; Presentation: EPA.]](/site/files/images/Figure-IW0.2_Large.jpg)
Wetlands are among the most biologically productive and diverse habitats on the planet (Environmental Protection Authority, 2004) and have a vital role in landscape functionality. At this time it is not possible to provide an overall assessment of wetland condition. Some WA wetlands of State, national and international significance are well researched and protected. The majority of wetlands are not well-documented and consequently there is little available information to determine condition. Most information is available for wetlands on the Swan Coastal Plain, as this area has been subject to ongoing development and other pressures (see 'Loss or degradation of wetlands'; Figure IW0.3). Approximately 17% of wetlands on the Swan Coastal Plain have high conservation significance and 14% are formally protected. Wetlands in the Wheatbelt region of the South West are also under significant pressure due to altered water regimes, salinisation, eutrophication, acidification, invasion of weed and feral species, and historical widespread land clearing. Limited but intensive monitoring of 25 regionally important wetlands indicates that 26% show recent deterioration with rapidly declining biodiversity (Cale, Halse & Walker, 2004).
![Figure IW0.3: Management categories of wetlands on the Swan Coastal Plain. [Data source: Department of Environment [ver. 2005]; Presentation: EPA.]](/site/files/images/Figure-IW0.3_Large.jpg)
Groundwater can be found across the State at varying depths beneath the land surface. It provides a common hydrological connection between catchments, wetlands and waterways. At this time it is not possible to provide an overall assessment of groundwater condition. Although hydrogeological information exists for some developed areas of the State (see 'Altered water regimes'), there is a general lack of information about broad aquifer condition, given the sheer extent of groundwater and its complex nature. In general it is recognised that groundwater has been degraded in areas developed for urbanisation, industry and agriculture, and is coming under increasing pressure through water mining and abstraction (see 'Water supply').
Thirty-three actions were identified for inland waters in response to the 1998 State of the Environment Report (Government of Western Australia, 1999). Fifty-five percent of the actions are incomplete, 36% are complete but have not been evaluated, and only 9% have been both completed and evaluated. Progression and evaluation of actions has been complicated by a gradual decline in monitoring, reduced funding for rehabilitation projects, and other perceived priorities for water resource management agencies. Improved monitoring and evaluation of inland waters is urgently required. The National Action Plan for Salinity and Water Quality and Natural Heritage Trust programs intend to progress monitoring of issues such as eutrophication, sedimentation, salinisation and other inland water ecosystem health measures.
4.1 Implement the State Water Quality Management Strategy no. 6: a policy to ensure inland waters are managed under an approved environmental management framework.
4.2 Finalise and implement the draft Waterways Western Australia Policy, with oversight by a waterways management committee that has community representation.
4.3 Develop and implement a State Wild Rivers Policy that also includes rivers of high conservation value.
4.4 Finalise and implement the revised Wetlands Conservation Policy for Western Australia.
