Mulgrave Basin

The Mulgrave basin contains the largest population centres in the region. At the northern end of the basin are the city of Cairns (population in excess of 170,000) and the Trinity Inlet. The Indigenous Yarrabah community with a population of approximately 3000 people is located on the coast to the east of Cairns. The Port of Cairns occupies the lower end of Trinity Inlet and provides limited deep-water ship berthing.

The upper catchment is in the relatively undisturbed rainforest environments of the Bellenden Ker Range. A small portion of the upper Mulgrave is on the edge of the developed agricultural area of the Atherton Tableland. The river floodplains and the lower river valley are dominated by sugarcane where the environment has been significantly modified with the loss of much of the original lowland rainforest.


Scroll down for further detailed results for each indicator group.



very good








very poor

insufficient data

Confidence surrounding the data used in the circle diagrams has been assessed using a multi-criteria framework.


Water quality

Hover over each segment for indicator scores and data confidence.

The overall water quality grade in 2015-16 for the Mulgrave Basin is ‘good’.

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 Deeral, capturing 59% of the basin.

The sediment score is comprised of a total suspended solids (TSS) score of 71.7 (‘good’) meaning that the annual median of TSS concentrations complied with guideline values.

Nutrients scored 45.9 (‘moderate’) in the Mulgrave basin, comprising of a DIN (Dissolved Inorganic Nitrogen) score of 29.9 (‘poor’) and FRP (Filterable Reactive Phosphorus) score of 62.0 (‘good’).

Using the ms-PAF method, pesticides received a low risk category with 2.64% of species affected in the waterways of the Mulgrave basin. This resulted in a pesticide grade of ‘good’ for the basin.

Compared to 2014-15 the water quality index for the Mulgrave basin remained ‘good’ but decreased from 72.2 to 63.5. The change was driven in part by a decrease in score for TSS and DIN.

Habitat and hydrology

Hover over each segment for indicator scores and data confidence.

The overall habitat and hydrology grade for the Mulgrave basin in 2015-16 is ‘good’.

The habitat modification score of 100 (‘very good’) is comprised of an impoundment length score of 100 (‘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.

The fish barrier indicator method is still being developed and will be available in future report cards.

Riparian extent for the Mulgrave basin scored 78.9 (‘good’) with 6.1% loss from pre-clear extent to 2013. With the basin predominantly rainforest in the upper and midlands, it is expected that the majority of loss is in the lowlands due to development and land use.

Wetland extent scored 34.8 (‘poor’) with 36.2% loss of palustrine (freshwater) wetlands from pre-clear to 2013. These results reflect a high level of historic loss due to development. Wetland losses in future reporting periods will be minimal.

Habitat modification, riparian extent and wetland extent are updated every four years and have not changed since 2014-15. The data for riparian and wetland extent are due to be updated in 2018.

The invasive weeds indicator is new for the 2015-16 period for which the Mulgrave basin scored 52.5 (‘moderate’).

The habitat and hydrology index score and grade differed between 2014-15 and 2015-16 due to the introduction of the invasive weeds indicator.

The method for the flow indicator is currently under development and will be available for future report cards.


Hover over each segment for indicator scores and data confidence.

The fish index is currently under development and will be available in future report cards.

Further information on the methods used to produce the scores and grades and detailed results can be found here.