Aquatic Ecology

Sustaining the ecosystems of our rivers, lakes, floodplains and wetlands is a fundamental objective of the Water Management Act 2000.

Our science team work to better understand how changes to water quality, volume and flow affect aquatic ecosystems. Understanding these relationships enables us to develop water sharing plans and policies that ensure sustainable and resilient ecosystems.

Many of these studies are collaborative projects with universities and other NSW and Commonwealth agencies.

How does water extraction impact aquatic ecosystems?

River flows in NSW naturally vary greatly from year to year and season to season. The plants and animals of our aquatic ecosystems are uniquely adapted to the extremes of drought and flood.

However, the flows of many NSW river systems have been significantly altered through water extraction and the construction of dams and weirs to provide water for irrigation, industry and town water supplies.

Regulating river flow and extracting water for use can change the variability of river flows including the natural wetting and drying patterns river systems.

For example, natural seasonal flows are often reversed in NSW river systems. Reduced high flows and flooding occur in late winter and spring from water being stored in dams and weirs. High flows of water are then released to downstream users in late summer when river systems usually experience low flows and drying. This water is also often much colder than usually occurs in these months causing what is known as cold water pollution.

Seasonal high river flows play a particularly important role for aquatic ecosystems.

They help:

  • trigger waterbird breeding and fish spawning
  • promote growth for riparian vegetation such as Red River Gums
  • prevent algal blooms
  • transport important nutrients and carbon used by fish and macroinvertebrates through the system

Regulated and unregulated river systems

River systems with storages such as dams and weirs that are operated to actively control flows are known as 'regulated' rivers. These storages can regulate or change the pattern of river flows in for many hundreds of kilometres. Most of the water extracted in NSW is from the regulated rivers.

For inland NSW, the regulated river catchments include the Border Rivers (which separates NSW and Queensland), Namoi, Gwydir, Macquarie, Lachlan, Murrumbidgee, Murray (which separates NSW and Victoria) and the Lower Darling River.

On the NSW coast, small regulating dams operate on the Richmond River in the north and the Brogo River in the south. Larger regulating dams in the Hunter Valley provide water for the irrigation, mining and power generation industries.

The Hawkesbury-Nepean River system has undergone significant alteration including the construction of Warragamba Dam to provide a safe and secure drinking water supply for the Sydney region. However, like many other coastal rivers that supply water for towns and industry, it is not classified as a regulated river. Water from storages in these systems are usually piped to towns and treatment facilities rather than released downstream. They can still have a significant impact on aquatic ecosystems by significantly reducing or changing natural flow patterns.

The term ‘unregulated river’ is applied to these rivers, as well as those with no storages. Water extraction may still occur in these river systems.

Groundwater systems

As with rivers, high levels of extraction can also affect our groundwater systems.

This can result in a permanent lowering of water levels allowing:

  • surrounding saline water to intrude into the aquifer
  • a reduction in the base flows to nearby rivers
  • a decrease in the water available to ecosystems that depend on the aquifer such as natural springs, limestone caves and surrounding vegetation

In an extreme case over-extraction could cause the aquifer to collapse.