Moresby Estuary

The area of the Moresby 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 3.3 km north and 2 km south of the river mouth along the coastline and extends approximately 12 km inland. The area includes numerous tributaries that drain into the main river channel.

Land use within the Moresby estuary area is dominated by cropping and pond aquaculture with some residential development. The Moresby locality is on the western fringe of the estuary area. The Port of Mourilyan is located near the mouth of the estuary and exports raw sugar and molasses from a loader, wharf and handling facility.

The Moresby estuary grade has remained ‘good’ and the score has decreased from 67 in the previous year to 65 in 2017-18 

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

Water quality

The Moresby estuary water quality changed from ‘very good’ to ‘good’ and the score decreased slightly to 79 from 81 in 2016-17. The lowest scoring indicators were DIN (dissolved inorganic nitrogen) (65), dissolved oxygen (69) and turbidity (69), and were graded ‘good’ whilst 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 five monitoring sites in the mid-estuary channels.  

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

Habitat and hydrology

The habitat and hydrology index is comprised of seagrass, which is updated annually, and three longer-term indicator categories that are updated every four years: mangrove and saltmarsh extent, riparian extent (both due for updates in 2018-19) and fish barriers (update due for 2019-20). The score for this index decreased to 51 from 53 the previous year, with the grade remaining stable at ‘moderate’.  

The mangrove and saltmarsh extent scored 79 (‘good’) with 5.9% loss from pre-clear to 2013. The riparian extent scored 64 (‘good’) with 13.2% loss from pre-clear to 2013.  

Estuary fish barriers for the Moresby estuary are scored 61 (‘good’) and are graded 'poor’ for barrier density, ‘good’ for percentage of stream length to the first barrier, and there is an absence of low passability barriers (graded ‘very good’).  

The seagrass at the Moresby River remained in very poor condition. The estuarine meadows in the Moresby estuary have now been completely lost and will require active restoration.   

  • In 2017-2018 no seagrass was present in the 5 monitoring meadows at Mourilyan Harbour/ Moresby Estuary. This is the first time since monitoring began (1993) that seagrass was absent from all monitoring meadows.  
  • Widespread loss of seagrass occurred in the zone in 2009-2010. Some initial recovery of colonising species occurred up until 2014-2015. Since then, seagrass condition has been very poor due to reductions in seagrass biomass and area. 

Mourilyan Harbour remains the only long-term monitoring location in the wet and dry tropics regions where no recovery of the foundation species has occurred following severe seagrass declines that occurred along Queensland’s east coast during the 2009-2011 period. 

The flow indicator could not be assessed for the Moresby estuary due to the lack of pre-development modelled flow and flow assessment sites, which are required for the analysis. 


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

See the detailed reports for further information on the methods used to produce the scores and grades and detailed results.