Marine
zones
Key findings for Cleveland and Halifax Bays from the 2026 Report Card
The Townsville Dry Tropics Waterways Report Card assesses waterway health from the catchment to the Reef, recognising that activities on land influence conditions downstream in coastal and marine environments. This includes areas in Cleveland Bay, Halifax Bay, and much further from the coast in the Offshore Marine Zone beyond Magnetic and Palm Islands.
Cleveland Bay water quality remained ‘good’ overall.
During the 2024-2025 reporting year, individual measures shifted across key indicators, however, the results balanced out across the zone, with Cleveland Bay receiving a similar overall score to last year.
​
The Magnetic Island sub-zone maintained a ‘good’ water quality grade. Nutrients continue to improve for the fourth consecutive year. Although still graded ‘moderate,’ this represents the strongest result since the Report Card began. Nutrient scores remain influenced by both elevated concentrations and stricter water quality targets that are applied within the Great Barrier Reef World Heritage Area. Physical-chemical properties declined slightly, driven by total suspended solids, which dropped from ‘very good’ to ‘good.’ Chlorophyll a improved, returning to a ‘very good’ grade.
​
In the Enclosed Coastal sub-zone, physical-chemical indicators decreased from ‘good’ to ‘moderate.’ This shift was driven by turbidity and total suspended solids in the Inside Port zone, which fell from ‘good’ to ‘moderate’ and ‘very good’ to ‘good,’ respectively. Sediment flowing north from the Burdekin River likely played a role, as did the timing of samples, such as on a strong incoming tide near the sandbar, which results in resuspension of sediment. Across the sub-zone, Chlorophyll a also fell from ‘good’ to ‘moderate’, marking the third year in a row of decreasing grades for this indicator.
​
The Open Coastal sub-zone showed a slight improvement overall, with grades increasing for both turbidity and secchi in the Outside Port zone.
Halifax Bay water quality declined from ‘good’ to ‘moderate.’
This change is influenced by the absence of data from the Enclosed Coastal sub-zone, which historically has supported a higher grade, often returning ‘very good’ water quality. Without this sub-zone, the overall score reflects conditions in the remaining two sub-zones.
​
Most improvements were seen in the Open Coastal sub-zone. Two measurements for nutrients (particulate nitrogen and particulate phosphorus) both saw a grade increase, lifting the overall nutrient score. Physical-chemical conditions also improved, with turbidity and total suspended solids both returning a ‘very good’ grade. As a result, the physical-chemical indicator increased from ‘moderate’ to ‘good.’
In the Midshelf sub-zone, chlorophyll a improved slightly, rising from ‘poor’ to ‘moderate.’
After the rain: why waters become cloudy
Turbidity and total suspended solids (TSS) are both measures of water clarity. Turbidity describes how cloudy the water appears, while TSS measures the amount of fine particles, such as sediment, organic matter, and algae, suspended in the water.
During heavy rainfall, runoff washes soil and other materials from the land into rivers and coastal waters. At the same time, higher flows, strong winds, and wave action can stir up sediments already on the seafloor, keeping them in suspension. Together, these processes increase both turbidity and TSS, making the water appear cloudy.
When rainfall is well above average, such as more than double typical annual totals, these effects are amplified, with more erosion, more runoff, and more sediment moving through the system. This keeps the water cloudy for longer, reducing the sunlight that reaches seagrasses and corals, which is essential for their survival. With habitats already under stress following heavy rains, these extended periods of low light limit opportunities for recovery, slowing the ability for marine habitats to bounce back.
In Cleveland Bay, the habitat indicator assesses both seagrass meadows and coral reefs. This year, the overall grade declined from ‘moderate’ to ‘poor,’ with both habitats rated ‘poor.’
Seagrass health dropped from ‘moderate’ to ‘poor,’ driven largely by a decline in density or the amount of seagrass growing in an area. However, the overall size of the meadows and variety of seagrass species recorded remained relatively stable, which is favourable for future recovery.
​
The loss in density seen across the region was influenced by widespread environmental pressures, such as periods of cloudy skies, strong winds, and high wave activity. All these conditions limit the amount of sunlight reaching the seagrass, and without enough light, seagrass struggles to grow.
​
When tough environmental conditions persist year after year, recovery becomes more difficult, as seagrass has limited opportunity to rebuild between events. Seagrass surveys were conducted before the record-breaking wet season and therefore do not reflect any potential impacts from this event.
​
Discover more about seagrass in our StoryMap - Guardians of the Bay.
Coral condition in Cleveland Bay remained ‘poor,’ marking the lowest score recorded since the Report Card began. In contrast, coral grades in Halifax Bay remained stable.
While corals were exposed to a range of stressors over the 2024-25 summer, associated with the record-breaking wet season, the current decline in condition reflects the effects of the 2024 mass bleaching event, which occurred the summer before.
​
Although bleached corals may still be alive at the time of surveys and are recorded as live coral, the longer-term outcome is only known when follow-up surveys observe whether coral colonies recovered or died.
​
Changes in coral communities were mixed across the seven reefs surveyed. The make-up of hard coral species declined at three reefs and remained stable at the other four. At Geoffrey Bay, both coral cover and the change in hard coral declined, with grades dropping from ‘moderate’ to ‘poor’, and from ‘good’ to ‘poor’, respectively. Havannah North also recorded a decline, receiving a ‘poor’ grade for change in hard coral.
​
Encouragingly, juvenile coral numbers, key to reef regrowth, improved from ‘poor’ to ‘moderate’ in Geoffrey Bay and at Pandora North, with Havannah North remaining ‘good.’ These young corals offer hope, helping reefs rebuild after disturbances when conditions allow.
​
Macroalgae (seaweed), which has been a concern for several years, showed some improvement. At Pandora South, macroalgae grades increased from ‘poor’ to ‘good’, while Pandora North improved from ‘very poor’ to ‘poor,’ indicating reduced seaweed cover compared to the previous year. These improvements were likely influenced by the severe weather, which physically removed macroalgae from reef surfaces.
​
Dive into our Corals of the Townsville Region StoryMap, to discover the reefs in Halifax and Cleveland Bays.
Offshore Marine Zone
Coral reefs in the Offshore Marine Zone, those furthest from the coast, remained in ‘good’ condition overall. Of the nine surveyed reefs, five showed signs of improvement, including John Brewer Reef, which continues to recover following an earlier crown-of-thorns starfish outbreak. The remaining four reefs declined slightly, although not enough to change their overall grade.
​
One notable result was recorded at Helix Reef, which is the first reef in the Dry Tropics region to receive a ‘very poor’ score for change in coral cover since the Report Card began. It is also the first reef to receive a ‘very poor’ rating for any coral indicator in the Offshore Marine Zone in the past two years.
Strong recruitment of juvenile, or baby, corals contributed positively to overall reef condition. All surveyed reefs scored ‘very good’ for coral recruitment, with counts at John Brewer Reef and Dip Reef improving from ‘good’ to ‘very good.’ This boost in juvenile corals helped lift Dip Reef’s overall grade from ‘moderate’ to ‘good.’ Across the region, six reefs are now graded ‘good,’ while three remain ‘moderate.’
​
Recent survey data for individual reefs and regions can be explored on the Australian Institute of Marine Science’s Reef Monitoring Dashboard. Their coral cover data is based on manta tow surveys, while the Report Card uses data from fixed site surveys.
​
Manta tow surveys assess coral cover along the reef slope and around the perimeter of a reef, providing a broad overview. In contrast, fixed site surveys focus on smaller areas to record greater detail. For nearly four decades, trained marine researchers have returned to the same spot at each reef surveyed to build a powerful picture of change over time.
