Barron Basin

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 declined from ‘good’ to 'moderate' with the score decreasing from 61 to 54. 

The diagram below shows the detailed results for each indicator by year. Click on the timeslider to see data from previous years.

Water quality

The water quality grade for the Barron Basin remained ‘good’ although the score decreased from 74 to 69.

The sediment score, comprised of the total suspended solids (TSS) indicator, scored 67 (‘good’) improving from ‘moderate’ the previous year. Whilst monthly median concentrations of TSS often exceeded guideline values during the short wet season (January to March) concentrations met guideline values for most of the other months.

Nutrients were graded ‘good’ and scored 71, slightly lower than the previous year.

Dissolved inorganic nitrogen (DIN) and filterable reactive phosphorus (FRP) and were graded ‘good’ with monthly median concentrations often meeting guideline values.

Sampling for pesticides was expanded in 2017-18 and 2018-19 in order to populate the Pesticide Risk Baseline, and dropped back to a more routine sampling regime in 2019-20 which did not include the Barron Basin.

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 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 Barron Basin habitat and hydrology index scored 46 for 2019-20 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 was 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 34 (‘poor’) 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).

In addition, an outbreak of the floating invasive macrophyte Amazon frogbit (Limnobium laevigatum) has occurred in the Barron since the previous assessment (2015-16). Mapping of Amazon frogbit in the Barron Basin from 2016 to 2019 has shown how rapidly new invasive weed species can spread through waterways.

More information on the Amazon frogbit in the Barron is available in the results technical report .

The Barron Basin grade for flows remained ‘good’ and scored 80. Flows in the Barron 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 at most sites.

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.

Fish

The freshwater fish assessment was conducted at 11 sites in the Barron Basin and the index grade was ‘moderate’ with a score of 48.

A total of 29 species were caught and included 13 translocated species (Australian species that do not naturally occur in the waterway) and two species introduced into Australia, the guppy (Poecilia reticulata) and spotted tilapia (Pelmatolapia mariae).

The indicator for species diversity scored 60 with a grade of ‘moderate’ meaning fewer native species were caught than expected.

The indicator for introduced fish species scored 35 and was graded ‘poor’ mainly due to high numbers of translocated Australian species caught.

Most of the Barron catchment is above the Barron Falls which is a natural barrier to fish movement. Consequently, the species diversity of fish in the catchment upstream of the Barron falls is naturally depauperate. The stocking of fish species into the Barron has been common practice and the fish fauna upstream of Barron Falls is one of the most modified in Australia.

Further information on the methods used to produce the scores and grades and detailed results