Mossman Basin

The Mossman Basin has an area of 479km2 with Mossman (~1,700 people) and Port Douglas (~3,200 people) being the major population centres. The basin consists of 76% natural/minimal use lands, 3% grazing, 10% sugarcane, 4% urban and 6% other land uses.

Steep mountains and hills dominate the Mossman Basin, with a narrow coastal plain which has been cleared and developed with agriculture (predominantly sugarcane) and urban land uses.

The Mossman Basin grade has remained ‘good’ although the score decreased from 67 in 2017-18 to 63 this year. 

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

Water quality

Water quality reporting for the Mossman Basin commenced in 2017-18 with monitoring conducted by Douglas Shire Council at five sites located upstream and downstream of the Mossman River and South Mossman River confluence. Monitoring was not conducted during high flow events and consequently freshwater basin condition was assessed from base-flow water quality data only.

Water quality in 2018-19 for the Mossman Basin scored 90 and the grade remained ‘good’.

The sediment score, comprised of the total suspended solids (TSS) indicator, was 90 and the grade improved from ‘good’ to ‘very good’ with monthly median concentrations of TSS mostly meeting the guideline values.

Nutrients were graded ‘good’, the same as 2017-18, and scored 66. Dissolved inorganic nitrogen (DIN) was graded ‘moderate’ with some monthly medians meeting guideline values. Filterable reactive phosphorus (FRP) was graded ‘very good’ with monthly median concentrations mostly meeting guideline values. The scores for DIN (42) and FRP (89) were very similar to the previous year.

Pesticides decreased from ‘good’ to ‘moderate’ and scored 60, equating to over 94 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 five Douglas Shire Council monitoring sites on the Mossman and South Mossman River, sampled during low flows only and capturing up to 86% 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 2019-20), instream habitat modification consisting of impoundment length (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 2018-19 includes the third year of reporting for the flow indicator. The Mossman Basin habitat and hydrology index scored 56 for 2018-19 and declined from ‘good’ in 2017-18 to ‘moderate’ due to the poorer score for the flow indicator.

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. There was no change in impoundment length score for the 2018-19 assessment.

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

Riparian extent for the Mossman Basin scored 68 (‘good’) with 11.5% loss from pre-clear extent to 2013. It is expected the uplands would generally have better extent due to protected areas and less development. Less extent in the lowlands is due to development and land use.

Wetland extent scored 16 (‘very poor’) with 60.7% loss of palustrine (freshwater) wetlands from pre-clear to 2017. An area of 0.6 hectares of palustrine wetlands was lost since 2013. These results reflect a high level of historic loss due to development.

The invasive weeds indicator scored 36 (‘poor’) in the Mossman Basin and represents substantial impacts of aquatic weeds within the Mossman freshwater system including hymenachne (Hymenachne amplexicaulis), salvinia (Salvinia molesta), water hyacinth (Eichornia crassipes) and pond apple (Annona glabra).

The Mossman Basin was graded as ‘good’ for flows during 2018-19. Flows in the Mossman River retained similar characteristics to modelled pre-development flows in their capacity to support the key ecological assets of water holes, low flow spawning fish, riffle habitats and fisheries production. More information on the results of the flow indicator is available in the results technical report. 


The fish index will be available for all basins in next year's 2021 Report Card.

See detailed reports for further information on the methods used to produce the scores and grades and detailed results