Realising the benefits of modern fish-protection screening in Australia

There has been significant progress in research, management and implementation in NSW (Fig. 1, Table 1). This includes informing design, supporting industry, coordinating action, engaging with stakeholders, and communicating outcomes. An incentive-based approach has been applied to initiate progress, showcase technologies, and generate evaluations opportunities (Rayner et al. 2023). Water users can self-nominate as ‘early adopters’, by an expression of interest (EOI) process, and receive financial, technical or institutional support to install screens. This approach is underpinned by lessons from international experiences and concepts from social-learning theory (e.g. Rogers 2003). It has been used to take action, on the basis of strong biophysical evidence (Boys et al. 2021a), in lieu of a quantitative prioritisation, which could consider ecological, economic, and socio-cultural factors at a variety of spatial and temporal scales.

Fig. 1.

Map of modern fish-protection screening sites in Australia to August 2024. The status of screen installations is indicated, including expressions of interest (EOI) from water users to participate in incentive programs. Specific location data were not available for four additional sites installed in southern Queensland under the Northern Basin Toolkit, nine private sites in Victoria, and two sites in the Australian Capital Territory.

NSW water users have responded enthusiastically to opportunities to participate in incentive programs and implementation is well underway. In total, 36 modern fish-protection screen installations were completed in NSW from 2018 to 2024, mostly in the northern Murray–Darling Basin (Table 2). Together, these protect an estimated 819,126 native fish per year and deliver up to 2600 ML of cleaner water to water users per day across 234.09 km² of irrigated agriculture (see Entrainment section below for calculations). Most of these installations were on small diversions (with a maximum pumping capacity of 1–16 ML day⁻¹), using stainless-steel cylinder screens with brushed or water-jet cleaning mechanisms. A larger diversion was screened with a T-shaped dual cylinder screen plus an array of four cone screens, totalling 800 ML day⁻¹ (Fish Screens Australia 2023). No gravity-fed diversions have been screened in NSW.

The rate of uptake has been accelerating, particularly since 2023, with over A$30 × 10⁶ invested in incentive programs (Fig. 2, Table 2). This is despite delays caused by flooding, access to labour in regional areas, and variation in the price of stainless steel (Sverdrup and Olafsdottir 2019). A further 12 installations have been funded and are in design and manufacture. Once installed, these will bring the total number of screened diversions in NSW to 48, protecting 1.72 × 10⁶ native fish year⁻¹ and delivering up to 5461 ML day⁻¹ of cleaner water (Table 2). A total of 26 additional water users have submitted EOIs. Screening of these sites would protect an additional 1.481 × 10⁶ native fish year⁻¹ and deliver up to an additional 4702 ML day⁻¹ of cleaner water per day, bringing the cumulative totals to 3.2 × 10⁶ native fish and 10,163 ML day⁻¹ (Table 1). However, demand has outstripped the quantum of funding available and further resources would be required to support screen installations at these latter 26 sites.

Fig. 2.

Uptake of modern fish-protection screening in NSW, indicating (a) cumulative number of sites, (b) cumulative maximum volume of cleaner water delivered per day, and (c) estimated cumulative number of native fish protected annually. Sites for 2025 are funded and set to be installed. Additional expressions of interest (EOIs) from water users to participate in incentive programs demonstrate the cumulative potential future uptake of modern screening technology.

Few screens have been installed in the southern portion of the NSW MDB and little attention has been given to coastal river catchments, as a consequence of funding availability. There is also a need to progress screening of gravity-fed diversions, which can entrain high numbers of native fish (Gilligan and Schiller 2003; Boys et al. 2021a). Advancing screening in these areas would require assessing the impacts of water diversions, prioritising sites, and understanding the stakeholders required for effective implementation. There are likely to be real and meaningful differences in the motivations and abilities of water users in coastal catchments versus inland systems, and between pumped and gravity-fed diversions, which will influence the uptake of screens (Rayner et al. 2023).

Progress in other jurisdictions has been limited, with few installations outside NSW. However, attention is shifting towards the challenge.

Evidence of native fish entrainment is well established. Boys et al. (2021a) used all available historical and contemporary scientific evidence to establish a conservative best estimate of 3.5 native fish ML⁻¹. That rate can be used to estimate the impacts of individual pumping sites. However, it is an approximation, which contains two key assumptions. Specifically, that pumps operate continually at their maximum daily capacity (ML day⁻¹) and that pumps are used for 90 days per year. A 90-day irrigation season is consistent with feedback gathered from irrigators and is considered appropriate. However, pumping rates are known to vary among days and seasons, according to variables such as local weather conditions, crop requirements and pump maintenance schedules.

Opportunities exist to strengthen understanding of the spatial and temporal variability in fish entrainment rates. Hutchinson et al. (2022) began tackling this challenge, by sampling 10 pumped and two gravity-fed diversions in southern Queensland. They reported a mean entrainment rate of 28 native fish ML⁻¹ across the pumped diversions (maximum pumping capacity ranged from 14 to 164 ML day⁻¹), likely driven by a relatively high density of native fish in these waterways (cf. Boys et al. 2021a). However, they also reported significant variation in entrainment rates among sites. These were driven by factors such as the diversion type (pumped versus gravity-fed), intake position and depth, pumping rate, river flow type, fish size and life-history stage (Hutchinson et al. 2022). Further research is underway across south-eastern Australia, including assessment of pump configurations, species vulnerability, seasonal variability and population-scale benefits of screening multiple diversions in a river reach.

Gravity-fed diversions typically entrain more native fish per megalitre than do pumped diversions (Boys et al. 2021a; Hutchinson et al. 2022). This difference is likely to occur because gravity-fed diversions extract a larger portion of the total flow (as high as 97% in some cases; Boys et al. 2021a) and may be perceived by fish as a natural branch in the river channel. A single irrigation offtake channel can entrain 5 × 10⁶ native fish, including their eggs and larvae, in a single irrigation season (Gilligan and Schiller 2003). This indicates that tens of millions of native fish are likely to be entrained across pumped and gravity-fed diversions in Australia every year and that the population-scale impacts are likely to be significant (Boys et al. 2021a).

Laboratory flume studies have explored the complex interactions between swimming abilities of fish species found in Australia, flow velocity and screens. Boys et al. (2013a) found that lowering approach velocities to 0.1 m s⁻¹ effectively reduced entrainment of both juvenile silver perch (Bidyanus bidyanus) and golden perch. Similarly, Stocks et al. (2019) found that a 2-mm wedge-wire screen eliminated entrainment of juvenile golden perch at 0.1 m s⁻¹, but impingement rates increased significantly with water velocity. Other species trialled include larval Murray cod (Stocks et al. 2024), golden perch (McSweeny 2021) and the invasive redfin perch (Perca fluviatilis; Doyle et al. 2023). Additional data are soon to be published, including small-flume testing 12 additional species (Joachim Bretzel, Charles Sturt University, unpubl. data) and a large-flume study, employing a high-volume channel, examining larval Murray cod and golden perch (Craig Boys, unpubl. data).

This body of research was used to define and validate the Design Specifications for Fish-Protection Screens in Australia (Boys 2021). The specifications account for screen location and orientation, hydraulics, construction, internal baffling, maintenance, and fish bypass design. Critically, the specifications recommend an approach velocity not exceeding 0.1 m s⁻¹ and a mesh size of 2–3 mm (Boys 2021). Field-based studies have demonstrated that screens built to these specifications can reduce entrainment of fingerlings by over 98% for native species (Bretzel et al. 2023) and confirmed the importance of approach velocity in governing fish entrainment (Boys et al. 2013b). Deviating from these standards will result in poorer fish protection and debris control, increased maintenance costs and an increased risk of screen failure.

Rigorous social research has informed strategic stakeholder engagement and effectively enabled the success of incentive programs in Australia. Unlike in other countries, such as New Zealand, there is no legislative requirement for modern fish-protection screens to be installed on water diversions (see Rayner et al. 2023). Uptake is being progressed by securing, and then capitalising on, the enthusiastic participation of water users, while simultaneously removing barriers to participation and implementation. This requires inter-disciplinary collaboration, integration of biophysical and social science, and the development of approaches to stakeholder engagement and communication, an approach that appears to be unique to Australia in the context of modern fish-protection screening.

For example, the NSW Government has created a stakeholder-centred approach to engagement, combining diffusion of innovations theory (Rogers 2003) with the motivations and abilities (MOTA) framework for stakeholder assessment (Conallin et al. 2022). The emphasis is on understanding ‘triggers’, ‘motivations’ and ‘abilities’ for adoption, the social context of conservation interventions, and the relationships and networks of communication among stakeholders. The aim is to establish genuine dialogues with stakeholders, understand their attitudes, perceptions and capacities, and work towards participatory co-design of initiatives. Irrigators in inland NSW, for example, are motivated to protect fish, save money and improve their social licence to operate (Nayeem et al. 2023a, 2023b). However, a range of barriers to adoption must also be overcome, using a variety of technical, governance and social solutions (Rayner et al. 2023).

Investment in fish screens returns market and non-market public and private benefits. Public benefits result from improved native fish populations, waterbird populations, recreational fishing and river ecosystem health (J. Rolfe, J. De Valck, M. Star, N. Flint, D. Rajapaksa, A. Rahman, M. Gordos and B. Blackwell, unpubl. data). For example, cost–benefit analysis (CBA) for a proposed A$15.2 × 10⁶ screening incentive program in NSW estimated a net present value (NPV) of A$52 × 10⁶, distributed across private and public stakeholders, with a benefit–cost ratio (BCR) of 4.7 to 1 (Boyd Blackwell, unpubl. data). On-ground works engage local businesses, drive job creation, and support agricultural productivity. High-quality, stainless-steel screens have an estimated lifespan of 50 years and annual maintenance costs estimated at 3% of the initial cost of just the screen component of a full site installation (Brett Kelly, AWMA Water Control Solutions, pers. comm.). Irrigators can also benefit from reduced backflushing of pumps to clear debris, and higher crop yields from reduced sprinkler blockages; together, these create water, energy and labour savings, and increased revenue.

The monetary value of public benefits derived from screening demonstrates that government support is appropriate and should continue. However, there is a definite role for private investment in the future of screening in Australia. Jaensch (2023) provided an analytic policy framework to identify scenarios where government investment is not only justified, but imperative for the optimisation of returns. The research found that a lower bound of A$177 of public benefits is derived per megalitre of water passing through a modern screen, but that subsidies of at least 70% are required to make screening projects viable for small farms (Jaensch 2023). Private co-investment can help improve the overall impact of screening programs, by allowing public funding to be directed to a higher number of diversions. Economic research is underway in NSW to quantify both private, on-farm benefits of screen installations (including savings in water, power, and maintenance and the value of improved social licence) and additional public benefits not yet captured (such as improvements to recreational fishing and cultural values).