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’ with the score increasing from 67 to 71 on 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 for the Johnstone Basin remained ‘good’ and the score increased from 75 in 2018-19 to 78.
Nutrients remained ‘good’ with a score of 70. Both the dissolved inorganic nitrogen (DIN) indicator (scoring 74) and filterable reactive phosphorus (FRP) indicator (scoring 66) remained ‘good’, with monthly median concentrations often meeting guideline values.
TSS (the indicator for sediment) was ‘very good’ and the score remained 90 with most monthly median concentrations meeting guideline values.
Pesticides for the Johnstone Basin remained ‘good’ with the score increasing slightly from 74 in 2018-19 to 76, equating to over 98 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 four longer-term indicator categories that are updated every four years: wetland extent, (updated for 2017-18), riparian extent (to be updated for 2020-21), instream habitat modification consisting of impoundment length (updated for 2018-19) and fish barrier indicators (in development), and invasive weeds (updated for 2019-20).
The annual scores for the habitat and hydrology index from 2014-15, 2015-16, 2016-17 represent the changes resulting from the addition of indicators and not changes in the indicator scores themselves, whilst the index scores for 2017-18 to 2019-20 include annual updates to the flow indicator as well as updates to the longer term wetland extent, impoundment length and invasive weeds indicators. The Johnstone Basin habitat and hydrology index scored 63 for 2019-20 and the grade improved from ‘moderate’ in 2018-19 to ‘good’.
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 was impounded by artificial structures.
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 24 (‘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 improved from ‘good’ in 2018-19 to ‘very good’. Flows in the Johnstone Basin retained similar characteristics to modelled predevelopment flows in their capacity to support the key ecological assets of water holes, low flow spawning fish, riffle habitats and fisheries production.
The flow indicator provides scores for each flow assessment site and this can be used to assess flows at more local scales. More information on the results of the flow indicator is available in the results technical report.
The freshwater fish assessment was conducted at 11 sites in the Johnstone Basin and the index grade was ‘good’ with a score of 72.
A total of 30 species were caught and included three translocated species (Australian species that do not naturally occur in the waterway) and four alien species (species introduced into Australia) - the guppy (Poecilia reticulata), the swordtail (Xiphophorus helleri), the platy (Xiphophorus maculatus) and spotted tilapia (Pelmatolapia mariae).
The indicator for species diversity scored 78 and was graded ‘good’ meaning native species expected to occur were frequently caught.
The indicator for introduced fish species scored 66 and was graded ‘good’ due to fairly low numbers of alien and translocated fish species caught.