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Water quality

Top findings

Nitrate-nitrogen concentrations were worsening (55 percent) at more monitored river sites
than improving (28 percent). Dissolved reactive phosphorus concentrations were improving
(42 percent) at more monitored river sites than worsening (25 percent).

E.coli concentrations affect our ability to swim in some rivers.

What is happening?

The main pressures on the quality of our fresh water result from land-based activities.

Water quality at sites where the upstream land cover is mainly urban and pastoral tends to be poorer than sites where native land cover is dominant. Urban and pastoral sites have higher nutrient (nitrate-nitrogen and dissolved reactive phosphorus) and E.coli concentrations, and lower visual clarity and macroinvertebrate community index scores.

Nitrate leaching from agricultural soils has increased, which may be associated with the worsening trends in nitrate-nitrogen at sites in catchments where pastoral land cover is dominant. We are seeing improving trends in dissolved reactive phosphorus at many sites where pastoral, urban, and exotic forest land cover are dominant.

Why does it matter?

When water quality declines, it influences the way people and communities use the water and the water’s ability to support freshwater ecosystems and social and economic activities. High nutrient concentrations can result in excessive plant and algal growth, which can reduce oxygen levels and change the composition of plant and animal communities. Low visual clarity, toxic algal blooms, and elevated E.coli concentrations negatively affect aesthetic values and our ability to use fresh water for drinking or recreation. Heavy metals (such as mercury, arsenic, cadmium, lead, copper, and zinc) can be toxic to freshwater fish and invertebrates and can accumulate in food sources like fish and watercress, which may make them unsafe to eat. Many activities that support our tourism industry also rely on good water quality.

Water quality is a complex concept related to the physical, chemical, and biological characteristics of water. Water quality relates to the ‘condition’ of water as it affects a range of water values, including biological habitat and human use (Davies-Colley, 2013).

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