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 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 in the Moresby estuary changed from ‘good’ to ‘very good’ with the score increasing slightly from 78 to 81 since 2015-16. The lowest scoring indicators for 2016-17 were dissolved oxygen (66) and DIN (dissolved inorganic nitrogen) (61). These 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 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). The Moresby estuary also includes seagrass which is assessed every year.

The habitat and hydrology score for the Moresby has decreased slightly from 54 in 2015-16 to 53 and is graded ‘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 'very good' for an absence of low passability barriers.

The seagrass at the Moresby River estuary has undergone the complete loss of some seagrass meadows and species, and there has been an absence of seeds or propagules for an extended period of time. There is little chance for the seagrass scores improving in this zone from very poor (scoring 7) without assisted restoration.

  • Seagrass condition in this zone has been very poor for the last 3 years, driven by an almost complete loss of seagrass biomass and area in Mourilyan Harbour.
  • Widespread loss of seagrass occurred in Mourilyan Harbour in 2009-2010. In 2014-2015 and 2015-2016, only the subtidal meadow (MH5) had returned. In 2016-2017, one intertidal meadow also returned (MH2), although this was a relatively small, low biomass patch compared to its previous extent.
  • The foundation species (Zostera muelleri and Halodule uninervis) that were present in monitoring meadows between 1993 when monitoring began, and 2009-2010 when seagrass loss occurred, remain absent.
  • Mourilyan Harbour remains the only long-term monitoring location in the wet and dry tropics region 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 lack of recovery in foundation species, despite improved growing conditions from 2012, is likely due to a lack of seagrass propagules. Seedbank surveys over the last four years have demonstrated very low densities of Z. muelleri seeds, and in 2015 and 2016 seeds were entirely absent. Assisted restoration is required to re-establish viable Z. muelleri in Mourilyan Harbour, given the lack of a seedbank and the absence of a healthy nearby source population from which seeds or propagules could disperse.

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.

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