Trinity Inlet

The area of the Trinity Inlet estuary reporting zone can be defined by the pre-cleared extent of mangrove and saltmarsh remnant vegetation which is characterised by species that require periodic inundation of sea water.

This area extends approximately 14 km inland south of the inlet’s mouth and is approximately 8 km in width. It includes numerous tributaries that drain into Trinity Inlet.

Land use within and adjacent to the Trinity estuary area includes residential, industrial and commercial developments associated with the central business district of Cairns.

Trinity inlet includes the Port of Cairns which is a multi-purpose port that caters for bulk cargo cruise shipping, fishing vessels and reef passenger vessels. Land use adjacent to the smaller upstream tributaries is dominated by cropping (sugarcane) with some residential development.

The Trinity Inlet estuary grade declined from ‘good’  to ‘moderate’ in 2023-24. Trinity Inlet and the surrounding catchment experienced extreme rainfall and flooding of waterways in December following landfall of Severe Tropical Cyclone Jasper.

Key results

• The water quality grade for Trinity Inlet declined from ‘good’ to ‘moderate’ and the score decreased from 69 to 59 since the previous year.
• Chlorophyll a declined from ‘good’ to ‘moderate’ and the score declined substantially from 76 to 41, with monthly medians of chlorophyll a concentrations sometimes exceeding guideline values. This represented substantially higher quantities of algae in the water column compared to the previous year.
• Dissolved inorganic nitrogen (DIN) declined from ‘good’ to ‘moderate’ whilst filterable reactive phosphorus (FRP) improved from ‘good’ to ‘very good’ since the previous year.
• Seagrass condition in Trinity Inlet declined from ‘moderate’ the previous year to ‘poor’. The decline was attributed to low light levels reaching seagrass beds due to above average rainfall and river flow in the 12 months prior to October-November 2023 monitoring. The decline in condition occurred before the extreme weather events in December 2023 from Tropical Cyclone Jasper.

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