Collie River - Collie River Road

River condition at the Collie River Road site (site code: CR153COLL1, site reference: 6121280 ‒ previously reported as site code: CR-06, site reference: 6121240) on the Collie River has been assessed as part of the Healthy Rivers program  using standard methods from the South West Index of River Condition (SWIRC). The SWIRC incorporates field and desktop data from the site and from the broader catchment. Field data collected include the following indicators, assessed over about a 100 m length of stream:

• Aquatic biota: fish and crayfish community information (abundance of native and exotic species across size classes, general reproductive and physical condition)
• Water quality: dissolved oxygen, temperature, specific conductivity, and pH (logged in situ over 24 hours), as well as laboratory samples for colour, alkalinity, turbidity and nutrients
• Aquatic habitat: e.g. water depth, substrate type, presence of woody debris and detritus, type and cover of macrophytes and draping vegetation
• Physical form: channel morphology, bank slope and shape, bioconnectivity (barriers to migration of aquatic species), erosion and sedimentation
• Fringing zone: width and length of vegetation cover within the river corridor and lands immediately adjacent, structural intactness of riparian and streamside vegetation
• Hydrology: measures of flow (velocity) at representative locations (compared against data from stream gauging stations within the system)
• Local land use: descriptions of local land use types and activities (compared against land use mapping information for the catchment)

The Collie River Road site was most recently assessed in March 2023. All known assessments are listed in Table 1 below:

Other data:
The Collie River Road site is about 2.5 km downstream of the Mt Lennard gauging station (site reference: 612006) on the Collie River. The gauging station is owned by the Department of Water and Environmental Regulation (the department) and has been in operation from 1973 to 1997, and from 2016 to 2022.

Search the site code or site reference in the department’s Water Information Reporting (WIR) system to find data for this site and nearby sampling points (flows, surface water quality, groundwater monitoring, department’s meteorological data). See also the Bureau of Meteorology website for additional meteorological data for the area.

The assessment site had optimal structural aquatic habitat complexity.

In-stream habitat was characterised by dense wood in various sizes throughout most of the site. Woody debris, particularly large logs, can provide shelter for small and large-bodied fish from fast flows as well as protection from aquatic and terrestrial predators. Additional habitat was provided by riparian vegetation draped into the water along almost the entire bank length. Vegetation draped in the water not only provides habitat for small fish and macroinvertebrates but can also be used as a source of food, with fauna able to directly feed on the vegetation or on the bacteria and algae that grow on it.

The riverbed consisted of bedrock, boulders, cobble, pebble, gravel, sand and silt. This provides refuge and surfaces for grazing by native fish and crayfish. The substrate had a high cover of organic material including algae, detritus and leaves, which provides food for grazers and macroinvertebrates.

Water quality measured over the 24-hour collection period (29–30 March 2023) was within optimal conditions for South West species. Dissolved oxygen was above the lower limit of 4 mg/L used in the SWIRC and had a diurnal range of 1 mg/L. Aquatic fauna can be at risk when dissolved oxygen concentrations drop below 4 mg/L, with such concentrations also harmful to basic ecological processes. The mean water temperature was 19.4°C and had a diurnal range of 2.2°C which is below the SWIRC upper guideline of 25°C and within the recommended diurnal range of 4°C. The low diurnal variability of dissolved oxygen and temperature is supported by stream shading provided by the riparian vegetation. Figure 1 shows the relationship between dissolved oxygen and temperature at the assessment site over the 24-hour sampling period.

FIGURE 1. DISSOLVED OXYGEN AND WATER TEMPERATURE RELATIONSHIP AT COLLIE RIVER ROAD SITE, MARCH 2023

The mean salinity at the Collie River Road site was 1461 mg/L, which is within the marginal brackish salinity category. This is elevated over natural conditions for the system; however, many of Western Australia’s South West freshwater fish species are found in water ranging between 500 to 2500 mg/L (Mayer et al 2005).

The species captured at the Collie River Road site during each of the sampling periods are provided in Table 2. The table includes a list of all species previously reported in the subcatchment, which provides an indication of species that may occur at the assessment site. As differences in habitat within a subcatchment naturally influence species distributions, and variability in methods between sampling programs can affect the species caught, this list is only indicative. Below are some of the notable findings from the assessments.

Eight species of fish and crustaceans were found in the March 2023 assessment. This includes four native freshwater fish (nightfish, western pygmy perch, western minnow, and freshwater cobbler), two native freshwater crustaceans (smooth marron and south-west glass shrimp) and two non-native freshwater fish (eastern gambusia and redfin perch).

Freshwater cobbler was the dominant fish species during the 2019 and 2023 assessments. They are the largest native freshwater fish species in the South West and prefer deeper water with complex habitat (particularly large woody debris and undercut banks). A range of size classes including juveniles were recorded during the 2023 assessment, with just more than half of the captured individuals measuring between 20–40 cm. This demonstrates that this section of the Collie River provides suitable habitat to support recruitment of freshwater cobbler.

The richness and abundance of smaller-bodied native freshwater fish species have been comparable over the past four sampling events. Many of the recorded species were in the larger size categories. However, one-quarter of the western pygmy perch catch during the 2017 assessment were juveniles. This suggests that the primary nursery habitats for most species exist elsewhere in the system.

It should also be noted that western pygmy perch were lower in abundance during the 2019 (three individuals) and 2023 (one individual) sampling events, with only fish in the larger size categories recorded.

Western pygmy perch are both common and highly catchable, so the lack of detection at this site is unusual. The reason for lower numbers in the recent studies is unknown but does not appear to be related to water or habitat quality given the presence of other species. The results could be attributed to many factors including sampling effort, preference for nearby habitats, and predation by or avoidance of the non-native redfin perch.

Redfin perch were introduced to Western Australia in the 1890s and have been well established in the Collie River for many years. A total of four and six individuals were captured during the 2019 and 2023 sampling events, respectively. Redfin perch are considered one of the most significant predators of native fish and crayfish in the South West. Further investigation and increased sampling efforts of western pygmy perch populations are recommended for the next scheduled sampling event in 2025‒26.

Although eastern gambusia were present within the Collier River system, they did not outnumber native species. Eastern gambusia can coexist with native fish species when the natural environment, such as water quality and aquatic habitat, have not been too disturbed.

Smooth marron were the only freshwater crayfish species during the 2023 sampling event. Gilgie have been found in very low abundance in previous assessment years (2017 and 2018). It is not uncommon for more than one species of crayfish to coexist in the same environment. Smooth marron typically relies on permanent waters, whereas gilgies can tolerate seasonal drying by digging burrows to the water table to avoid desiccation. The absence of gilgies in 2019 and 2023 is not a significant concern but should be monitored over future sampling events.

Note: collection of fauna from inland aquatic ecosystems across Western Australia requires a licence from the Department of Primary Industries and Regional Development (DPIRD) and the Department of Biodiversity, Conservation and Attractions (DBCA). All species collected must be reported to these agencies as part of licence conditions.

Although not directly targeted as part of the Healthy Rivers assessment, the following species were recorded:

• Carter’s freshwater mussel (Westralunio carteri) – listed as vulnerable under the Biodiversity Conservation Act 2016
• South-western snake-necked turtle (Chelodina oblonga) – one individual recorded in 2023

Freshwater mussels play an important role in freshwater ecosystems as they can maintain water quality by removing sediments and pollutants through filtration (Beatty et al. 2017).

For more info on these and other aquatic species, please see the River Science fauna page.

References and further reading
Beatty SJ, Ma L, Morgan DL and Lymbery A (2017). Baseline assessment of Carter’s Freshwater Mussel, Westralunio carteri at proposed bridge construction sites on the Lower Vasse River. Centre for Fish and Fisheries Research Group and Fish Health Unit (Murdoch University).

Bennett K & Green A 2011, Environmental flow regime for the lower Collier River – Wellington reach, Environmental water report series, Report no. 22, Department of Water and Environmental Regulation, Western Australia.

Mayer XM, Ruprecht JK and Bari MA 2005, Stream salinity status and trends in south-west Western Australia, Department of Environment, Salinity and Land Use Impact Series, Report No. SLUI 38.