Water Pollution in the Great Barrier Reef

Our beautiful Great Barrier Reef is threatened by water pollution from land-based activities like agriculture.  

Our Reef needs to be strong in the face of rapidly warming oceans. Land-based pollution is a preventable problem entirely in our control. We must stop water pollution and give our Great Barrier Reef the clean water it needs to restore its health.

The water pollution problem

Water pollution is considered as one of the highest risks to the Great Barrier Reef’s health, impacting critical habitats for threatened dugongs, turtles and fish. After decades of inaction by the agricultural sector to stop pollution, water quality of our inshore Reef has remained in poor condition.

While climate change remains the biggest threat to our Great Barrier Reef, we need to clean up the water that flows from the land to reduce further pressure and help it recover.


Water Quality and Land-based Runoff

Runoff refers to the excess water that flows across the surface of the land or into groundwater and into nearby creeks and rivers after rainfall or irrigation. Runoff can often wash fertilisers, pesticides and sediment from the land into bodies of water.

All waterways and creeks eventually lead to our oceans. The runoff of these pollutants from agriculture is, therefore, a major threat to inshore coral reefs and seagrass meadows in our Great Barrier Reef.

Excessive fertiliser applied to crops, like sugar cane, can wash into rivers and waterways, and ultimately out to the Great Barrier Reef. Nitrogen from these fertilisers is linked to harmful algal blooms, which can block sunlight, reducing corals’ resilience to bleaching and coral diversity. Algal blooms can also reduce the amount of light available required for seagrasses to grow and be healthy.

Pesticides and herbicides have been detected in high concentrations in inshore areas of the World Heritage Area and pose a further risk to marine plants and animals. Herbicides are applied to crops to kill weeds by inhibiting their ability to grow. But when they wash into the Reef, they also inhibit the growth of other non-target plants, such as seagrasses, on which dugongs, turtles and fish depend.

Tree clearing and overgrazed grasslands cause soils to erode and wash into creeks and rivers that run into the Great Barrier Reef.

Sediment discharged from rivers reduces sunlight available to seagrasses and corals, which can smother coral and seagrass growth. To reduce the sediment smothering our Reef, we need to protect and restore the land and maintain plant cover, especially along our rivers.

Satellite image of Fitzroy River flood plume, Queensland on the 8th of April 2017.
Photo credit: European Space Agency Sentinel 2 Mission

Crown-of-thorns starfish (COTS) are marine invertebrates that feed on coral. Whilst they occur naturally on our Reef, when conditions are right outbreaks can occur. COTS outbreaks can cause widespread damage to our Reef, including loss of coral cover and decline in biodiversity.

Many scientific studies have investigated what causes outbreaks of COTS and have found it is likely to be a combination of factors. A study found that the survival of COTS larvae increases dramatically when algae, their food source, becomes more abundant. Nutrient pollution from land-based run-off can cause algal blooms and provide the required boost in food source for COTS.

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Tackling water pollution is entirely within Queensland’s control. The solution is to start making changes on our land before it ends up in our waterways. 

In 2019, the Queensland government passed a historic bill designed to improve water quality flowing into our Reef from agricultural properties.

We all support our farmers and graziers to make changes on their land. The new regulations target those practices that pose the greatest risk for water quality, such as farmers who are overusing fertiliser and polluting our Reef. 

We urge the Queensland Government to achieve a high level of compliance with these regulations, that are crucial for the future of our Reef and the thousands of jobs it supports in Queensland.

In addition, our Governments also need to urgently establish an adequately funded coastal wetland restoration and protection program to improve water quality; Rehabilitation of just 5% of a land parcel to wetlands can reduce nitrogen pollution by 20-50%! Follow the link below to find out more about the super powers of wetlands: