Collie River - River Road Bridge

River condition at the River Road Bridge site (site code: CR165COLL1, site reference: 6121281‒ previously reported as site code: CR-07, site reference: 6121241) 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 River Road Bridge 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 4 km downstream of the Wellington Flume gauging station (site reference: 612013) on the Collie River. The gauging station is owned by Water Corporation and managed by Harvey Water.

Search the site code or site reference in the Department of Water and Environmental Regulation’s (the department) 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 moderate density of wood in various sizes throughout most of the site ranging from small twigs/sticks to large fallen trees. 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 feed directly on the vegetation or on the bacteria and algae that grow on it.

The riverbed consisted of 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 19.5°C and had a diurnal range of 3.2°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 THE RIVER ROAD BRIDGE SITE, MARCH 2023

The mean salinity at the Collie River Road site was 1443 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 River Road Bridge 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.

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

Notably no non-native species were recorded in the 2023 assessment.

Smooth marron was the dominant catch. Marron require permanent, good quality water and prefer areas with complex habitat (particularly woody debris). A wide range of size classes were recorded with more than half of the population having a carapace size of 20–50 mm (generally less than two years old). This demonstrates that this section of the Collie River provides suitable habitat (including water quality) to support successful recruitment.

Gilgie were not found in 2023 but have been found in very low abundance in previous assessment years (2009 and 2017). It is not uncommon for more than one species of crayfish to coexist in the same environment, though smooth marron often dominate permanent waters. The absence of gilgies in 2018, 2019 and 2023 is not a significant concern as could be a function of naturally low abundance and sampling effort, but this should be monitored over future sampling events.

Nightfish, western minnow, western pygmy perch and freshwater cobbler were all present at this site in similar abundance. Freshwater cobbler were the only species to have juveniles present within the catch.

A general absence of juveniles of the small-bodied native fish species has been identified over the majority of the sampling events. The reason(s) for this is not clear, particularly as water quality is good, and as the site provides complex habitat. This may be related to the availability of nursery habitat. Each of these species prefers to move into smaller habitats through winter and/or spring (such as shallow tributaries or floodplains containing complex shelter) and lay eggs on or around inundated vegetation. The Wellington Dam prevents upstream migration, and the high, continuous flow regime created by dam releases does not allow for periodic inundation of vegetation. The high water clarity provided by releases may also increase the success of predators (with the reach known to contain established populations of the exotic redfin and trout species).

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.

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).

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.

Water Corporation, Wellington Dam. Retrieved June 1, 2023