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

Water quality

Water quality for the Trinity Inlet estuary changed from ‘very good’ to ‘good’ with the score decreasing from 83 to 78 since 2015-16. The lowest scoring indicator for 2016-17 was dissolved oxygen (41) which was graded moderate. DIN (dissolved inorganic nitrogen) was graded ‘good’ and all other indicators were graded ‘very good’.

Water quality grades are based on aquatic ecosystem guidelines for protection of estuarine waters, and are not based on load reduction targets for the marine environment. The results are derived from a transect of eight monitoring sites in the channel of Trinity Inlet.

Pesticides are not monitored in the Trinity Inlet estuary therefore a score and grade cannot be provided.

Habitat and hydrology

The habitat and hydrology index is comprised of three longer-term indicator categories that are updated every four years: mangrove and saltmarsh extent (update due for 2017-18), riparian extent (update due for 2017-18) and fish barriers (update due for 2019-20). Trinity Inlet also includes seagrass which is assessed every year.

The habitat and hydrology score for Trinity Inlet has increased from 48 in 2015-16 to 50 and is graded ‘moderate’.

The mangrove and saltmarsh extent scored 53 (‘poor’) with 20.6% loss from pre-clear to 2013. The riparian extent scored 57 (‘moderate’) with 17.6 per cent loss from pre-clear to 2013. These results reflect the high level of development within the estuary area of Trinity Inlet. The low mangrove and saltmarsh extent scores for Trinity Inlet are mostly the result of historic extensive clearing activity. More recently mangrove communities in the Trinity Inlet estuary have been effectively managed to ensure there has been no major new clearing and to allow for some revegetation.

Estuary fish barriers for Trinity Inlet are scored 61 (‘good’) and are graded 'moderate’ for barrier density, ‘moderate’ for percentage of stream length to the first barrier and 'very good' for an absence of low passability barriers.

The seagrass at Trinity Inlet experienced almost complete loss after cyclones and severe flooding in 2009-2011. Seagrass condition in this zone has improved since then but has remained poor for the last 3 years. The score has increased from 21 in 2015-16 to 30. Trinity Inlet has two subtidal meadow sites (CN19 and CN33) and one intertidal meadow site (CN20). Poor overall condition was largely due to the following.

  • The complete loss of meadow CN20 in 2014-2015 and 2016-2017 and, in 2015-2016, that meadow’s reduced area relative to the baseline.
  • Poor meadow area of CN33 over the past two years.
  • Very poor species composition condition in 2014-2015 and 2015-2016 in meadow CN19 due to the reduction in Halophila ovalis relative to the more colonising species Halophila decipiens.

The flow indicator could not be assessed for the Trinity Inlet estuary due to the lack of pre-development modelled flow, which is required for the analysis.


The fish index is currently under development and will be available in future report cards.

Further information on the methods used to produce the scores and grades and detailed results can be found here.