The Johnstone Basin population is 15,000 and largely concentrated within the towns of Innisfail, Malanda, Millaa Millaa and South Johnstone.
The two key tributaries of the Johnstone River include the North Johnstone and South Johnstone Rivers. The North Johnstone River Basin can loosely be divided into three sections.
The upper river is a ‘mixed land use’ area consisting of dairy, beef grazing, sugar cane, horticulture (potatoes) and the townships of Millaa Millaa and Malanda.
The middle section contains steep forested areas, much of which is in the Wet Tropics World Heritage Area.
The lower reaches are characterised by low sloping hills and coastal floodplains, which contain a majority of the agricultural areas including the larger townships of Innisfail and South Johnstone.
The Johnstone Basin has an area of 2,326 km2 and has a relatively high proportion of natural/minimal use lands (55%). The remaining area contains 16% grazing, 12% sugarcane, 6% dairy (in the upper catchment), 3% bananas, 1% other crops, 2% urban and 4% other land uses.
The Johnstone Basin grade has remained ‘good’ and the score of 67 was unchanged from 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.
The water quality grade in 2018-19 for the Johnstone Basin remained ‘good’ with the score increasing from 69 in 2017-18 to 75.
The dissolved inorganic nitrogen (DIN) indicator scored 72 and remained ‘good’, with monthly median concentrations often meeting guideline values. Filterable reactive phosphorus (FRP) scored 69 and remained ‘good’, with monthly median concentrations mostly meeting guideline values.
TSS (the indicator for sediment) scored 90 and the grade improved from ‘good’ in 2017-18 to ‘very good’, with most monthly median concentrations meeting guideline values.
Pesticides for the Johnstone Basin remained ‘good’ with the score increasing from 61 in 2017-18 to 74, equating to over 97 percent of species protected for the risk assessment metric.
Water quality grades are based on aquatic ecosystem guidelines for protection of freshwater systems and are not based on load reduction targets for the marine environment. Except for pesticides the results are derived from two end of catchment monitoring sites at Goondi (North Johnstone River) and Central Mill (South Johnstone River), capturing 58% of the basin. Pesticide results are derived from the Coquette Point monitoring sites, capturing 70% of the basin.
Habitat and hydrology
The habitat and hydrology index is comprised of the flow indicator category (updated annually) and four longer-term indicator categories that are updated every four years: wetland extent, (updated for 2017-18), riparian extent (to be updated for 2019-20), instream habitat modification consisting of impoundment length (updated for 2018-19) and fish barrier indicators (in development), and invasive weeds (to be updated for 2019-20).
The annual scores for habitat and hydrology index for 2015-16 and 2016-17 represented changes due to the addition of the invasive weeds and flow indicators, respectively, and not changes in the indicator scores themselves. The index score for 2018-19 includes the third year of reporting for the flow indicator. The Johnstone Basin habitat and hydrology index scored 59 for 2018-19 and the grade declined from ‘good’ in 2017-18 to ‘moderate’ due to the poorer score for the flow indicator.
The habitat modification score of 98 (‘very good’) is comprised of an impoundment length score of 98 (‘very good’) indicating that less than 1% of the total length of the waterways with a stream order of 3 or higher are impounded by artificial structures. There was no change in impoundment length score for the 2018-19 assessment.
The fish barrier indicator method is still being developed and will be available in future report cards.
Riparian extent for the Johnstone Basin scored 74 (‘good’) with 8.1% loss from pre-clear extent to 2013. It is expected that the majority of loss is in the lowlands due to development and land use.
Wetland extent scored 25 (‘poor’) with 45.2% loss of palustrine (freshwater) wetlands from pre-clear to 2017. There was no recorded loss of wetland area since the last assessment in 2013. These results reflect a high level of historic loss due to development.
The invasive weeds indicator scored 29 (‘poor’) in the Johnstone Basin and represents substantial impacts of aquatic weeds within the Johnstone freshwater system, including hymenachne (Hymenachne amplexicaulis), salvinia (Salvinia molesta), and pond apple (Annona glabra).
The Johnstone Basin grade for flows declined from ‘very good’ in 2017-18 to good. Flows in the Johnstone Basin retained similar characteristics to modelled pre-development flows in their capacity to support the key ecological assets of water holes, low flow spawning fish, riffle habitats and fisheries production.
The fish index will be available across all basins in the next 2021 Report Card.