Great Barrier Reef health update - 19 February 2025

Reef Health update | 19 February 2025 © Great Barrier Reef Marine Park Authority

As the lead managers of the Great Barrier Reef, the Reef Authority keeps an eye on the Reef year-round — with efforts stepped up over summer, a typically high-risk period from extreme weather.

The Reef Authority releases updates on the health of Reef which includes; sea surface temperatures, rainfall and floods, cyclones, crown-of-thorns starfish outbreaks, and coral disease.

These updates are based on forecasts, water temperature heat mapping, in-water surveys, citizen science and aerial surveys.

Reef Health update | 19 February 2025

The impacts of the recent heavy rainfall and flooding across north Queensland are continuing to be assessed, including any changes to the Great Barrier Reef's water quality.

Major to moderate flooding levels have been observed across nearly all river basins covering over 500 kilometres of coast between Cairns and Mackay. Significant flood plumes have been detected entering the Reef lagoon from all affected river systems some of which extend from the inshore to mid-shelf reefs.

The recent low-pressure systems across the Great Barrier Reef in the past weeks did have a cooling effect on sea surface temperatures.

Despite the cooling effect, sea surface temperatures in all regions of the Marine Park remain above historical averages. In the Northern and Central areas of the Marine Park this cooling has been short lived.

Temperatures

Sea surface temperatures have cooled across the Marine Park but continue to exceed historical averages.

The forecast for March indicates sea surface temperatures will remain 0.5-1-degrees Celsius above average across the Reef.

Rainfall

Rainfall is likely to continue to be above average across much of Northern Australia from March to May.

Reef health

Over the past fortnight, 175 Reef Health Impact Surveys (RHIS) were conducted across 19 reefs in the Marine Park. These surveys provide a detailed snapshot of reef health, including a breakdown of habitat and impact assessment.

Reefs surveyed in the Northern, Central and Southern regions showed low levels of coral bleaching—1 to 10% bleaching prevalence. No data was available for reefs in the Far Northern Region.

The Marine Monitoring Program is out sampling sites in the Mackay-Whitsundays, Burdekin, and Wet Tropics areas following the heavy rainfall over the past few weeks. Aerial and satellite imagery is being used to view and assess the flood plume extent, which is expected to move north and east.

Nutrient and sediment-rich, low salinity waters discharging from rivers after heavy rainfall can be detrimental to Reef health, increasing susceptibility to coral disease and bleaching. Prolonged exposure to these waters over the coming weeks could significantly impact the Reef in some locations through reduced light and promotion of algal blooms over large areas.

These stresses can contribute to localised seagrass and coral mortality.

As of last week, crown-of-thorns starfish (COTS) outbreaks were most severe in the Southern Region (Swain Reefs) and between Port Douglas and Lizard Island. Isolated and less severe outbreaks are persisting offshore Townsville and the Whitsundays. The COTS Control Program is continuing to suppress outbreaks and protect coral across hundreds of reefs.

Reef management

As the lead managers of the Reef, we are working closely with our partners to monitor conditions across the Marine Park during these high-risk summer months.

We also use a range of management actions to support and build Reef resilience, including enforcing compliance with our zoning plan and ensuring people enjoy the Reef in a responsible way.

The Marine Monitoring Program informs managers and the wider community about the condition of inshore corals and seagrass, and the effects of poor water quality from land-based runoff on these ecosystems.

The program is coordinated by the Reef Authority, with key partners including AIMS, James Cook University—TropWater, the Cape York Water Partnership, and University of Queensland.

You too can help by reporting any incidents through the Eye on the Reef app, which is available for download on Google Play or Apple Store.