Johnstone Estuary

The area of the Johnstone 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 1.5 km north and 2 km south of the river mouth along the coastline and extends approximately 5.4 km inland.

The area includes numerous tributaries that drain into the main river channel. The assessment area of riparian extent extends further up the river than the mangrove and salt marsh communities to the upper tidal limit and includes vegetation types that are more typical of freshwater environments.

Land use within and adjacent to the Johnstone estuary area is dominated by residential and other urban developments and cropping. Urban development is associated with the town of Innisfail which overlays sections of the estuary area.

The Johnstone estuary grade has remained ‘good’ in 2023-24 and the score of 61 declined slightly from 62 from the previous year.

Key results

• The water quality grade for Johnstone remained ‘good’ and the score increased slightly from 66 to 67 since the previous year.
• Dissolved inorganic nitrogen (DIN) declined from ‘poor’ to ‘very poor’ whilst grades for all other water quality indicators were unchanged compared to the previous year.
• The flow indicator for the Johnstone estuary remained ‘good’ although the score decreased from 71 to 61 mainly resulting from poorer scores for measures of flow variability due to above average rainfall, particularly the heavy rainfall events during December 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.