The Barron Basin has an area of 2189 km2 with Mareeba and Atherton as the main population centres.
The basin consists of 29% natural/minimal use lands, 31% grazing, 18% forestry, 8% other crops (including bananas), 3% sugarcane, 3% dairy, 5% urban and 4% other land uses.
The Barron River is the most modified river in the Wet Tropics region and is heavily regulated by water supply infrastructure.
The basin has a large upper catchment on the Tablelands and a smaller lower catchment north of Cairns where it discharges into Trinity Bay.
A major dam is situated at Tinaroo Falls at the northern end of Lake Tinaroo. The Barron River is a strong story place for Aboriginal custodians.
The Barron Basin grade has remained ‘good’ with the score of 61 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 Barron Basin remained ‘good’ with the score (69) similar to the previous year.
The sediment score, comprised of the total suspended solids (TSS) indicator, scored 55 (‘moderate’) decreasing from ‘good’ the previous year. Monthly median concentrations of TSS frequently exceeded guideline values during the wet season and the very high rainfall events leading to flood events were likely to have increased erosion and suspension of sediment.
Nutrients were graded ‘good’ and scored 76, similar to the previous year. Dissolved inorganic nitrogen (DIN) was graded ‘good’ with monthly median concentrations often meeting guideline values. Filterable reactive phosphorus (FRP) was graded ‘very good’ with monthly median concentrations mostly meeting guideline values.
The pesticides grade of ‘very good’ was unchanged since the previous year. The score of 89 equated to greater than 99 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. The results are derived from the end of catchment monitoring site at Myola, capturing 89% 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 Barron Basin habitat and hydrology index scored 47 for 2018-19 and the grade remained ‘moderate’.
The habitat modification score of 36 (‘poor’) is comprised of the impoundment length indicator showing 7.7% of the total length of the waterways with a stream order of 3 or higher are impounded by artificial structures. Tinaroo Dam is the largest impoundment in the basin. 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 Barron Basin scored 68 (‘good’) with 11.1% loss from pre-clear extent to 2013. It is expected that the majority of loss is due to development and land use.
Wetland extent scored 11 (‘very poor’) with 73.2% 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 56 (‘moderate’) in the Barron Basin and represents some impacts of aquatic weeds within the Barron freshwater system including hymenachne (Hymenachne amplexicaulis), salvinia (Salvinia molesta), water hyacinth (Eichornia crassipes) and pond apple (Annona glabra).
The Barron Basin grade for flows improved from ‘moderate’ in 2017-18 to ‘good’. Flows in the Barron 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.
More information on the results of the flow indicator is available in the results technical report.
The fish index will be available across all basins in the next 2021 Report Card.