Great Barrier Reef Water Quality Is Improving in Many Rivers, New Study Finds

Water pollution has long threatened the parts of the Great Barrier Reef closest to shore, as sediment washed from farmland settles on seagrass and inshore corals while fertiliser runoff feeds algae that can damage coral health. A new study led by researcher Cassandra S. James, published in the Journal of Environmental Management, reports that water quality is now improving in many rivers flowing into the reef.

The team analysed up to 37 years of monitoring data from seven major river systems, tracking dissolved inorganic nitrogen from fertiliser and suspended sediment. These river basins drain roughly two-thirds of the reef's water catchments, an area about the size of New Zealand. The study found small but measurable improvements in nitrogen and sediment at most monitoring sites, with the Herbert, Burdekin, Pioneer, Tully and Fitzroy rivers among those showing long-term gains, often in bursts tied to shifts in rainfall, cyclones, land use or fertiliser practices.

A companion study examined the cause, using fertiliser-application data for key cropping areas from 1910 to 2024. Synthetic fertiliser use peaked in the 2000s and 2010s and has since fallen in many sugarcane- and banana-growing regions. In 2024, usage was 25-49% lower than each region's peak, even as crop yields stayed steady. Researchers say the decline likely reflects a mix of improved farm management, land-use change and rising fertiliser costs.

The authors caution the gains do not mean these rivers are now healthy: nitrogen and sediment levels in many still exceed thresholds suitable for wetlands, seagrass and nearshore coral reefs, and the reef still faces pressure from climate change, extreme weather and land clearing.

Since 2014, Australia's federal and Queensland governments have spent more than A$5 billion on catchment programs to improve reef water quality. Trends in nitrogen and sediment will feature in a progress report Australia must submit to UNESCO in 2028, under monitoring in place since the reef's 1981 World Heritage listing.