Inshore Central

The northern boundary of the Central inshore reporting zone area extends north-east from Cape Grafton just south of Cairns to the offshore boundary and includes enclosed coastal, open coastal and mid-shelf waters.

The southern boundary of the Central zone extends due eastward from the mainland just south of the Moresby River at Double Point to the boundary of the offshore waters.

The major rivers discharging into the central zone are the Mulgrave River the Russell River and Johnstone River. The Moresby River discharges into the southern coastal area of the Central zone. Numerous smaller waterways drain coastal sub catchments that discharge into the Central zone.

Water quality in the Central zone is affected by plumes of sediments, nutrients and pesticides from rivers discharging directly into the zone but also from the plumes of southern rivers, particularly the Tully/Murray, which are carried north by prevailing currents.

The area includes Fitzroy Island to the north, the High Island Group some 12km north-east of Deeral, the Frankland Island group approximately 16 km due east of Deeral and Normanby Island located between the High Island group and the Frankland Island group. These islands provide fringing shallow water environments that support coral reef ecosystems.

The overall grade for the Central zone in 2023-24 declined from ‘good’ to ‘moderate’ and the score decreased from 63 to 54 since previous year.

Key results

• The water quality grade in 2023-24 for the Central inshore zone remained ‘good’ and scored 61, decreasing from 71 in the previous year.
• Total suspended solids (TSS) declined in grade, from ‘very good’ to ‘good’ since the previous year.
• Oxidised nitrogen (NOx ) had a very substantial decline in grade from ‘good’ to ‘very poor’, whilst grades for particulate nitrogen (PN) declined from ‘poor’ to ‘very poor’ and particulate phosphorus (PP) declined from ‘good’ to ‘moderate’, since the previous year.
• Chlorophyll a, improved from ‘moderate’ to ‘good’ since the previous year.
• Higher concentrations of NOx, PN and PP typically occurred during wet season months and peak concentrations occurred in the December sampling occasions that coincided with the high discharge from the Russell-Mulgrave river systems that followed Tropical Cyclone Jasper.
• During the wet season, nutrient concentrations were highest at sites closer to the rivers’ mouth.
• Coral of the Central zone was impacted by crown-of-thorns starfish predation, thermal bleaching, along with storm waves and freshwater inundation associated with Tropical Cyclone Jasper.
• The coral condition index remained ‘moderate’ whilst the score decreased from 55 to 48 since the previous year.
• Coral cover grade remained ‘good’ but decreased substantially in score at several sites due to at least one of the impacts.
• Macroalgae score continued to decrease and dense mats of red macroalgae have continued to accumulate at High East, Franklands West, and Fitzroy West.
• Crown-of-thorns starfish on reefs in the Central zone were recorded at higher numbers than the previous year and densities reached ‘outbreak’ levels at several sites.

The diagram below shows the detailed results for each indicator by year. Click on the timeslider to see data from previous years.