Declining water quality

Both Great Barrier Reef Outlook Reports identified the declining quality of water entering the Great Barrier Reef over the last decade as a major threat to the ecosystem.

The Reef continues to be exposed to increased levels of sediments, nutrients and pesticides. In particular, there are significant effects in inshore areas close to developed coasts, such as mangrove die-back and increased algae on coral reefs.

The Reef receives run-off from 35 major catchments that drain 424,000 km2 of coastal Queensland. Most sediment entering the Great Barrier Reef comes from catchments in major pastoral areas such as the Burdekin, Herbert and Fitzroy Rivers.

The catchments that deliver water into the Great Barrier Reef can be divided into:

  • Coastal catchments that provide a continuous flow of freshwater to the Reef from small catchments supporting intensive farming e.g. Tully River and Pioneer River
  • Large catchments that drain large inland grazing areas and tend to be seasonal and influenced by flooding e.g. Fitzroy River.

There are major programs dedicated to improving water quality entering the Great Barrier Reef, including the Reef Rescue package and the Reef Water Quality Protection Plan and the marine monitoring program. However, it is likely to be decades before the full benefits of these initiatives are seen.

Scientific consensus statement

As part of the development of the Reef Water Quality Protection Plan 2013, a multidisciplinary group of scientists reviewed and synthesised advances in scientific knowledge of Great Barrier Reef water quality issues.

The scientific consensus statement concluded that key Great Barrier Reef ecosystems are showing declining trends in condition due to continuing poor water quality, cumulative impacts of climate change and increasing intensity of extreme events.