Mulgrave Basin

The Mulgrave Basin contains the largest population centres in the region.

At the northern end of the basin is 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.

The Mulgrave Basin grade has remained ‘good’ in 2023-24 and the score decreased from 74 to 67.

Key results

• The water quality grade for the Mulgrave Basin remained ‘good’ and the score of 72 was the same as the previous year.
• Dissolved inorganic nitrogen (DIN) and filterable reactive phosphorus (FRP) remained ‘moderate’, and sediment, comprised of the total suspended solids (TSS) indicator, remained ‘very good’.
• The habitat and hydrology index declined from ‘good’ to ‘moderate’ due to a decrease in score for the flow indicator.
• The flow indicator declined from ‘good’ the previous year to ‘moderate’ and this was due to higher-than-average rainfall events in July and December compared to years with more typical rainfall patterns.
• The fish index for the Mulgrave declined from ‘very good’ to ‘good’ with the score decreasing from 84 to 69. This was mainly due to an increase in the proportion of pest fish numbers caught, which included an additional two species (Mozambique tilapia and swordtail).

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