Land-based run-off remains the greatest contributor to poor water quality in the inshore areas of the Great Barrier Reef and is a major contributor to the current poor state of many inshore marine ecosystems.
Since European settlement, Reef water quality has declined due to coastal development and agricultural activities in adjacent catchments. The main water quality pollutants in land-based run-off that pose a threat to the Reef are primarily from agricultural activities in the catchments and include:
- Fine sediment
- Excess nutrients
- Pesticides (herbicides, insecticides and fungicides) and other pollutants.
On 17 February 2021, the Authority released a position statement on water quality in the Great Barrier Reef:
Poor water quality is a major threat to the Great Barrier Reef, particularly inshore areas. Improving the quality of water entering the Marine Park is critical and urgent. The Great Barrier Reef Marine Park Authority supports actions that reduce pollutant loads from all land-based sources.
The position statement outlines key pollutants contributing to the decline of water quality on the Reef and their impacts on Reef ecosystems.
There are 35 major catchments draining into the Great Barrier Reef Region, many of which have been highly modified for agriculture activities. Grazing lands are the main contributor of fine sediment and particulate nitrogen on the Reef. Sugarcane crops are the primary source of excess nutrients (dissolved) and pesticides. Other agricultural industries (e.g. horticulture), urban areas, sewage treatment plants, aquaculture activities, mining, industrial areas, ports, and defence activities also contribute pollutants across the Region. This can include coal dust, petroleum hydrocarbons, heavy metals, marine debris and microplastics, pharmaceuticals and personal care products.
The Authority acknowledges efforts to improve land management practices by landholders and the community in partnership with governments, natural resource managers, industry, research and conservation groups. There has been some progress towards achieving water quality targets in the Reef 2050 Water Quality Improvement Plan. However, there remains an urgent need to implement innovative and targeted actions to further improve the quality of water entering the Reef from all land-based sources.