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’ and the score increase from 63 to 74.  

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 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 2019-20 for the Mossman Basin scored 78 and the grade remained ‘good’.

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

Nutrients were graded ‘good’, the same as the previous years, and scored 66. Dissolved inorganic nitrogen (DIN) was graded ‘moderate’ with some monthly medians meeting guideline values. Filterable reactive phosphorus (FRP) was 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 Mossman 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 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 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 Mossman Basin habitat and hydrology index scored 68 for 2019-20 and improved from ‘moderate’ to ‘good’ due to improved scores for the invasive weeds and flow indicators.

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 was 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 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 for Mossman Basin scored the highest of all the basins (81) and was graded ‘very good’ following the Douglas Shire Council’s targeted control program of invasive aquatic weeds. The program successfully removed salvinia (Salvinia molesta) and water hyacinth (Eichornia crassipes) from most known locations in waterways (including artificial impoundments) of the Mossman Basin.

The Mossman Basin remained ‘good’ for flows during 2019-20. Flows in the Mossman River 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. More information on the results of the flow indicator is available in the results technical report.

Fish

The freshwater fish assessment was conducted at 13 sites in the Mossman Basin and the index grade was ‘good’ with a score of 77.

A total of 22 species were caught including two species introduced into Australia, the guppy (Poecilia reticulata) and swordtail (Xiphophorus helleri). The indicator for species diversity scored 55 and graded ‘moderate’ and represented fewer native species caught than expected. The indicator for introduced fish species scored 100 and was graded ’very good’ due to very low numbers of alien fish caught (species introduced into Australia) and no translocated fish caught (Australian species that do not naturally occur in the waterway).

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