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 diagram below shows the detailed results for each indicator by year. Click on the timeslider to see data from previous years.
Water quality in the Johnstone estuary remained ‘good’ with the year-on-year score increasing from 63 to 73. However, the 2016-17 water quality index did not include dissolved oxygen, and it was low concentrations of dissolved oxygen that received the poorest score for 2015-16.
For 2016-17 the lowest scoring indicator was DIN (dissolved inorganic nitrogen) at 48 (‘moderate’). FRP (filterable reactive phosphorus) and pesticides were graded ‘good’, and chlorophyll a was 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 five monitoring sites in the mid estuary and a Catchment Loads Monitoring Program site at Coquette Point in the lower estuary.
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 habitat and hydrology index for the Johnstone has increased from 51 in 2015-16 to 58 (both years graded ‘moderate’). The change is due to the addition of the flow indicator.
Mangrove and saltmarsh extent scored 63 (‘good’) with 13.7% loss from pre-clear to 2013. These results reflect some development within the estuary area.
Riparian extent is assessed to the upper tidal limit of the river which extends upstream of the estuary area that is characterised by mangroves and saltmarsh. Riparian assessment therefore includes areas that have been cleared for agriculture and other developments. The riparian extent scored 9 (‘very poor’) with 77.3% loss from pre-clear to 2013.
Estuary fish barriers for the Johnstone estuary scored 81 (‘very good’) and are graded 'very good’ for barrier density, ‘good’ for percentage of stream length to the first barrier and 'very good' for an absence of low passability barriers.
With regards to flows during 2016-17, the Johnstone estuary was graded ‘very good’. Flows to the Johnstone estuary were similar to pre-development flows in their capacity to support the key ecological assets of water holes, low flow spawning fish, riffle habitats and fisheries production.
More information on the results of the flow indicator is available in the results technical report.
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.