Key environmental pressures

It was drier than the preceding year. No major cyclones made landfall and there was less rainfall in the catchment and less river discharge flowing into the Reef than average. This was a welcome reprieve after major flooding in and around Townsville and further north the year before.

How did this affect inshore water quality?

  • Regionally, water quality was good in the Wet Tropics, good in the Burdekin and poor in the Mackay-Whitsunday regions
  • Individual water quality indicators are monitored annually for compliance with water quality guideline values. The good news is that in general, concentrations of chlorophyll a and total suspended solids have improved in most regions over the last five years. Both parameters met guideline values in most regions last year. Some types of nutrients also met guideline values in most regions last year.
  • In contrast, Secchi depth (an indication of water clarity) exceeded guideline values in all regions last year. Some types of nutrients exceeded guideline values as well.
  • Pesticides were detected frequently at the five monitored sites, although mostly at very low concentrations. There were no individual exceedances of guidelines.

Water quality trends since 2005

Inshore water quality - ambient results and trends

Inshore water quality: ambient results and trends

  • Water quality in the Reef varies with distance from the coast and major rivers but is also influenced by oceanic processes and forces like winds, currents and tides.
  • Removing the variability associated with wind, tide and season statistically reveals long-term trends in water quality. Water quality has declined since 2008 in the Wet Tropics region but shows early signs of improvement in the last 2 years.
  • Water quality has declined slightly in the Burdekin region since 2010.
  • Water quality has declined steadily in the Mackay-Whitsunday region since 2008.

What is monitored and where?

Inshore water quality is monitored for:

Wet season water quality monitoring

Wet season monitoring in the Great Barrier Reef 2019-20

Inshore water quality Cape York

Inshore water quality - Cape York region - science seminar

  • total suspended solids, turbidity, and Secchi depth (indicators of water clarity)
  • chlorophyll a (a measure of phytoplankton abundance, which responds quickly to nutrients)
  • nutrients (dissolved and particle forms of nitrogen, phosphorus, and carbon) and pesticides
  • temperature and salinity time-series.

View the Water quality sampling locations 2019-20

How do we monitor?

Water quality samples are taken year-round, at the surface of the water and below it. Sample sites extend seaward away from river mouths into inshore waters of four major regions: Cape York, Wet Tropics, Burdekin, and Mackay-Whitsunday.

Instruments called ‘loggers’ are moored at sea to record temperature, salinity, chlorophyll, and turbidity throughout the year .

In the wet season, we use satellite imagery to track the movement of flood plumes, and we ground-truth satellite information by sampling within the plume.

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