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.

Key results for 2024-25

The Mulgrave Basin grade has remained ‘good’ in 2024-25 with the score increasing from 67 to 69.

• Water quality remained ‘good’. The score was also unchanged at 72.
• Pesticide risk remained low.
• Dissolved inorganic nitrogen (DIN) and filterable reactive phosphorus (FRP) remained ‘moderate’.
• Sediment, comprised of the total suspended solids (TSS) indicator, remained ‘very good’.
• The habitat and hydrology index improved from ‘moderate’ to ‘good’ due to an increase in score for the flow indicator.
• Wetland extent remained ‘poor’. No further loss of wetland habitat was recorded since 2019.
• The flow indicator improved from ‘moderate’ to ‘good’ since the previous year due to the return of a more typical rainfall pattern for the region including the timing of the wet season rainfall and flow events. Poorer scores were recorded in 2023-24 due to the influence of Severe Tropical Cyclone Jasper (TC Jasper) with the early onset of the wet season and intense rainfall and flood events from mid-December.

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