a coral surrounded by green algae


Excess nutrients, such as nitrogen and phosphorus, can cause algal blooms that turn the water green.

Nitrogen and phosphorus are found either attached to other particles, such as sediment, or dissolved in the water. Particulate nutrients are generally heavier and sink out of the water close to the coast, while dissolved nutrients are rapidly taken up into the reef’s ecosystem.

Our research

AIMS has been monitoring water quality in the Great Barrier for four decades. Since 2005, we have sampled nutrients in the reef’s inshore waters through the Great Barrier Reef Marine Monitoring Program. The results are used to track progress against targets in the Reef 2050 Water Quality Improvement Plan and the Reef 2050 Long Term Sustainability Plan.

We supplement this inshore water quality monitoring with regional models, including eReefs, to predict how water quality will respond to climate change and improvements in catchment management.

Condition / status

Elevated levels of nutrients are being discharged into the reef’s coastal waters, due to increased erosion, as well as fertiliser use in the catchment.

This is supported by evidence from:

  • changes in nitrogen and phosphorus river loads informed by catchment modelling and river monitoring
  • reef water quality monitoring and satellite remote sensing images
  • nitrogen and phosphorus signatures in cores of reef sediment and corals


Large amounts of nutrients, such as nitrogen and phosphorus, can cause algal blooms that turn the water green.

Nutrients can also harm reef ecosystems by:

  • increasing turbidity and reducing the light available to seagrasses, symbiotic coral algae and other reef organisms
  • potentially contributing to outbreaks of crown-of-thorns starfish, one of the main causes of coral cover declines on the Great Barrier Reef, by increasing the food for starfish larvae 
  • increasing coral disease and mortality
  • contributing to loss of coral diversity and algal dominance of reefs

Nutrient effects are managed by reducing end-of-catchment nutrient loads and assessing concentrations against relevant water quality guideline values. 

Supporting sustainable agriculture

AIMS appreciates that sugarcane and cattle farming are important to the economy, jobs, and the vibrancy of many coastal communities.

A quarter of Australia’s agricultural production occurs in Queensland. The state’s sugarcane and cattle farms generate $6.7 billion, more than half the value of the state’s agricultural production.

Our connection with farmers tells us they care about the reef. Many farmers are already adopting best management practises.