Menindee Lower Darling-Baaka Temporary Tube Fishway Trial

Australian native fish require unimpeded access along waterways to survive and reproduce. Different fish move within waters at different times to access food and shelter, to avoid predators, and to seek out mates. Some species such as Golden Perch can migrate thousands of kilometres while others only need to move a short distance.

Regardless of scale of movement, barriers to fish passage prevent the ability of native fish species to move and can have severe implications for these populations. In extreme cases, barriers can result in localised extinctions.

The Lower Darling-Baaka and Menindee Lakes are highly productive systems that support significant populations of native fish, especially following flow events that can create an ecosystem boom.

As new fish move into the Lower Darling-Baaka with inflows from the Northern Basin, the lakes provide ideal habitat and food for fish to grow, improve their condition and be ready for further movement opportunities on warmer waters

Currently in the Lower Darling-Baaka, fish can only migrate upstream as far as Lake Wetherell and Menindee Main Weir, with regulators and weirs blocking fish passage and contributing to significant increases in fish biomass, especially in the Menindee town weir pool.

The tube fishway trial is an exciting opportunity to test innovative fishway technology at such a significant scale on Australia’s native fish to help reduce fish biomass in the Menindee town weir pool.

The aim of the project is to test options to connect the Northern and Southern Basin, helping move some fish out of the Menindee town weir pool to complete their life cycle, and contributing to reducing the biomass in the weir pool, reducing associated risks for water quality and fish kills.

Due to the complexity of the existing weirs and regulators that allow flow management throughout the Menindee Lakes system, the design of effective fish passage solutions through the system can present significant challenges. Unfortunately, there is no one size fits all solution to restore fish passage in this system.

This exciting trial is about finding a cost-effective temporary solution while a Business Case for permanent fish passage is progressed with partner agencies to find effective and permanent fish passage solutions. This trial will provide valuable insights to inform potential long-term fish passage solutions.

The temporary tube fishway trial project will be undertaken on the Lower Darling-Baaka River near the Lake Wetherell Outlet Regulator. The location of the fishway is primarily driven by river operations and fish responses to try and maximise outcomes. When flows from are released from the top lakes they are primarily released from Lake Wetherell Outlet, which will be attracting fish to this point. The fishway entrance will be placed near the outlet flow to aid fish attraction and movement opportunities upstream via the tube fishway. The fishway exit will be placed in deeper sections of Lake Wetherell away from the inlet to help with the safe passage of fish upstream.

DPIRD Fisheries engaged NSW Public Works to manage the procurement process for the project’s construction services in accordance with the Department’s procurement guidelines via an open tender process that closed in September. The submitted tenders were then evaluated by a panel of experts based on select criteria and cost, with Fishheart Ltd the preferred tender.

Fishheart is a floating hydraulic fishway system that helps fish move past large barriers. Fishheart can be positioned to maximise the attraction of fish from river flows into the chamber. Artificial intelligence can then be used to detect and collect fish in the chamber, gathering data and informing flow operations in the tubes to propel fish up and over large weirs and dams.

A key advantage of the Fishheart design is that all output elements of the unit are adjustable. The flow rate of velocity used for attracting and passing fish will be assessed and adjusted based on site conditions. Importantly, the design allows for all the water used to transport fish to be taken from and returned to the upper reservoir (in this case Lake Wetherell) at the completion of the transportation of the fish as part of the movement cycle. The use of water from Lake Wetherell will also be informed by water levels in the lake and water quality, with the aim of the trial not to impact these aspects.

This type of fishway technology has not been tested locally at this scale yet; however there have been some smaller scale experiments and trials done. These local trials have been promising on smaller scales, with international examples including in Europe and in the USA that involve larger scale dams and several different species and sizes/shapes of fish also showing plenty of promise in the technology. Further research is needed to test this locally on large scales, and that’s the intent of the tube fishway trial project.

The trial will operate over the next 3 years (up to), commencing summer 2024/25 with the fishway in operation for up to 6-month periods (conditions pending) over spring/summer during this time. Operation of the fishway will be stopped over the autumn/winter periods due to reduced movement of fish naturally during this time. Any decision on progressing the trial will be made at the end of the project dependent on outcomes, conditions and funding.

In-built fish trapping capacity and the ability to differentiate between species and separate invasive species from native fish were included in the tender as preferred criteria for additional consideration. The Fishheart unit has the capacity for inbuilt fish trapping, as well as the ability to differentiate between species and separate invasive species from native fish. This technology offers the opportunity to differentiate and remove Carp as fish move upstream. Given the novelty of the Fishheart unit in Australia the primary focus in Year 1 will be on moving fish upstream and adjusting the technology as needed, with the potential to explore Carp separation and removal activities in later years.

Lake Wetherell Outlet Regulator is a very popular public access area, especially for camping, fishing and other recreational activities. Access to the broader area will not by impacted, including road traffic over the outlet regulator; however, access to the project footprint will be restricted. The project footprint will be kept as small as possible to minimise issues and will be identified by the security fencing (on land) and buoy line (on water). Primary focus for restricting access to the project footprint is from a WHS perspective as well as to protect the outcomes from the project. The final footprint will consider location specifics including cultural assessment information and recreational aspects such as boat ramp access.

Bed level survey work has been done upstream and downstream of the Lake Wetherell Outlet Regulator to help identify the deepest points for placement of the fishway that will maximise opportunities for fish attraction and movement over the largest range of flows. These opportunities are reliant on the flows coming out of Lake Wetherell Outlet Regulator. The project team will work closely with partner agencies and community to manage water security, to understand flow operations and implications during the trial periods.

Additionally, flood mitigation is a key consideration for the fishway trial, with actions built into the project to remove elements of the fishway and related infrastructure ahead of forecast flood events to reduce any potential damage or site issues.

The project will have minimal to no impact on vegetation in the project area focusing on already disturbed areas, noting that there may be some trimming of trees needed to for truck/crane access, but this will be minimal and avoided where possible. Cultural site assessment will be undertaken to identify and culturally sensitive sites and assets in the area, with avoid/mitigation actions where needed to protect these areas.

The effectiveness of passing fish and the condition of fish passed through the system, as well as any other species entrained is a primary focus of associated ecological monitoring being undertaken by the contractor and DPIRD Fisheries researchers. The monitoring and evaluation component led by DPIRD Fisheries researchers will be covered by an Animal Research Authority under the Animal Care and Ethics Committee (ACEC), and we’ll keep the community regularly updated on these aspects. If issues do occur with fish health and other impacts, there will be mitigation actions undertaken to reduce risks and impacts.

Actions have progressed and plans are in place for site works for the Lower Darling-Baaka Tube Fishway Trial project to commence on Monday 16 December 2024. The Fishheart team, contractors, Barkandji River Rangers and staff from WaterNSW, DPIRD-Fisheries and Public Works will be out at the Lake Wetherell Outlet Regulator to mark out the site, erect security fencing and start preliminary construction work.

During this time access will be restricted in the area, and please be aware of signage and fencing to stay safe whilst this exciting project commences. Pending how construction goes, planning is still underway to have the Fishheart fishway operational by the end of January 2025 to help move fish and connect the Northern Basin and Southern Basin.

The tender criteria requested that the fishway design allow for the passage of a broad range of species and size classes, including small-bodied species and juveniles (approximately 100mm), medium body fish such as Bony Herring and up to large-bodied adult Golden Perch and Murray Cod (with an expected maximum length of approximately 1200mm and head diameter of approximately 250mm).

Recent testing of the Fishheart in the United States successfully and safely passed fish in a size range from 112mm (Bluegill) all the way up to Longnose Gar (1145mm) and Blue Catfish (1130mm), showing promising potential for the Lower Darling-Baaka trial.