Dickson Inlet: Wet Tropics Waterway Health, North Queensland

The area of the Dickson 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 6.5 km north-east and 3.5 km south of the inlet mouth along the coastline and extends approximately 3.3 km inland. The area includes several coastal tributaries that drain into the Inlet.

Land use within the Dickson Inlet estuary area is dominated by residential and tourism service developments. There is a marina located within the Inlet.

The town of Port Douglas (population 3,205) is located within the estuary area and is a major tourism centre which attracts many national and international visitors each year.

The Dickson Inlet estuary grade has remained ‘good’ in 2021-22 with the score decreasing from 77 to 68 since the previous year.

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 Dickson Inlet estuary water quality declined from ‘very good’ to ‘good’ and the score decreased from 82 to 71 since 2020-21.

The lowest scoring indicator was dissolved oxygen which declined from ‘very good’ in 2020-21 to ‘moderate’, with monthly median values sometimes meeting guideline values. Chlorophyll a declined from ‘very good’ in 2020-21 to ‘good’, with monthly median values often meeting guideline values. All other indicators remained ‘very good’ with most monthly median values meeting guideline values.

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 six Douglas Shire Council monitoring sites in the channel of Dickson Inlet.

Pesticides are not monitored in the Dickson 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 and shoreline habitat updated in 2021-22), riparian extent (updated in 2021-22) and fish barriers (updated in 2021-22). The habitat and hydrology score declined from 74 in 2020-21 to 72 (graded ‘good’).

Mangrove and saltmarsh scored 67 (‘good’). Shoreline mangrove habitat scored 60 (‘moderate’), whilst mangrove and saltmarsh extent scored 75 (‘good’) with 8% loss from pre-clear to 2019.

Riparian extent scored 49 (‘moderate’) with 24% loss from pre-clear to 2019. There was no change to mangrove and saltmarsh extent or riparian extent between the previous assessment for 2017 and the updated assessment for 2019. These results reflect the surrounding development which has occurred along the fringe of the estuary area.

For estuary fish barriers, Dickson Inlet declined from 100 (‘very good’) to 80 (‘good’) due to the identification of a single barrier in the assessable waterways of the estuary zone.

Although seagrass habitat occurs in Dickson Inlet there is currently no seagrass monitoring at the estuary and a seagrass grade and score is not available.

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