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’ and the score decreased from 64 in the previous reporting period to 61 in 2017-18.
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 2017-18 for the Barron Basin was ‘good’ with the score decreasing in 2017-18 to 78 from 81 the previous year.
The sediment score, comprised of the total suspended solids (TSS) indicator, was 68 (‘good’) with monthly median concentrations of TSS often meeting the guideline values.
Nutrients were ‘good’ scoring 79, with dissolved inorganic nitrogen (DIN) and filterable reactive phosphorus (FRP) both graded ‘good’ and their monthly median concentrations often meeting guideline values.
Pesticides for the Barron Basin were reported for the first time. Pesticides were graded 'very good' and scored 87, equating to 99.4 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 2018-19), instream habitat modification consisting of impoundment length (to be 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 2017-18 includes the second year of reporting for the flow indicator and the updated wetland extent indicator. The Barron Basin habitat and hydrology index scored 45 for 2017-18 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.
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 was graded as ‘moderate’ for flows during 2017-18. Flows in the Barron Basin were substantially altered from pre-development flows at flow assessment sites downstream of the major impoundment of Tinaroo Falls Dam on the Barron River and Copperlode Dam on Freshwater Creek. The alteration of flow from pre-development conditions is likely to be a result of the impoundments and water extraction activity.
The fish index is currently being rolled out for the basins in the Wet Tropics and will be available for the Barron Basin in upcoming report cards.