March 4 Speaker Report: Wayne McLaren

Improving Fish Passage in the Barwon and Moorabool Rivers

The Society President, Harry Roberts, opened the evening by reflecting on the changing meaning of heritage. Once centred almost entirely on buildings, monuments and material relics, the concept now embraces the full legacy we inherit from our forebears: the geology that shapes our landscapes, the plants and animals that define our ecosystems, and the environments we pass on to future generations. Protecting heritage today means not only conserving what remains, but repairing what has been damaged and preventing the loss of species and ecological function.

It was in this broader spirit that Harry introduced our speaker, Wayne McLaren, who has spent twelve years with the Corangamite Catchment Management Authority, specialising in waterway restoration and rehabilitation. Wayne expressed his appreciation for the Society’s interest and support, noting that the work is federally funded and part of a much larger national effort to restore river health.

The Challenge: Restoring Fish Passage

Wayne began by outlining the scale of the problem. The decline of migratory fish is not unique to the Barwon or Moorabool—globally, around 80% of migratory fish populations have been lost, largely due to modified river systems and water extraction. Built structures such as weirs, dams, bridges, culverts, levees and road crossings interrupt the natural movement of fish, preventing them from completing their life cycles.

In our region, 15 reasonably common native species rely on unimpeded movement. Some spawn in the lower estuarine reaches but must travel upstream to grow and mature. Others undertake extraordinary migrations: the short‑finned eel, for example, travels from the Barwon all the way to the Coral Sea to breed.

Four species are considered nationally significant, with the Australian Grayling highlighted as a priority. Remarkably, the Barwon River holds one of the strongest populations of Grayling in Australia. Other key species include short‑finned eels, Tupong, and the ancient, filter‑feeding Lamprey.

Identifying the Barriers

The CCMA’s assessment process is methodical and evidence‑based:

• 800 potential barriers were initially identified across the catchment.
• Remote assessment and scoring criteria narrowed these to the highest‑risk structures.
• Field appraisals were conducted on the top 100.
• Biological assessments considered species needs and environmental conditions.
• Economic assessments estimated the cost and feasibility of remediation.

From this, the top 25 priority barriers were selected. Among the most significant are the Lower Barwon Barrage (on both sides) and Buckley Falls.

The Solution: Fish Ladders and Connectivity

Wayne explained the science behind fish ladders—structures that create a series of small pools, allowing fish to ascend obstacles gradually. Seven design types exist, and the CCMA works closely with Charles Sturt University and other partners to refine dimensions such as pool width, depth and flow.

The results have been remarkable. At the Barwon Barrage: 700,000 fish were recorded using the new passage in early monitoring and two million fish used it in the first full year. Wayne noted that fish numbers in the lower Barwon are now higher than at any time in the past century, particularly, just upstream of Lake Connewarre.

Monitoring is continuous, with three traps checked daily both upstream and downstream, providing the data needed to demonstrate ecological recovery.

Current Major Project: Buckley Falls (2025–2028)

Buckley Falls has been identified as the highest priority barrier in the Corangamite region. The project aims to restore 50 km of instream connectivity, with design options also being developed for Baum’s Weir.

Design Considerations

The site is physically constrained, with significant vegetation and public access.
The riverbed is shaped by ancient basalt flows, creating complex hydraulics.
Both European and Aboriginal cultural heritage must be respected.

Upstream Design

The preliminary concept addresses a 4.5‑metre drop using a long series of pools with 100 mm increments. Removing the existing concrete capping reduces the required height and allows the design to use natural pools where possible, achieving a gentle 1:30 gradient.

Downstream Design

A different approach is required, aiming to maintain a naturalistic flow while still enabling fish movement.

Related Sites

Baum’s Weir: Work is planned to correct earlier modifications and address the twin channels that once fed the paper mill and flour mill races.

Batesford Weir: Its future is under review, with removal a possibility if it is no longer required.

Monitoring and Evidence

Fish sampling uses multiple methods to determine how many fish currently pass each barrier. Early results show that very few fish make it beyond the major structures, reinforcing the importance of the planned works. Baseline data is essential so that improvements can be measured accurately once construction is complete.

Discussion and Questions

Questions from members ranged from the abundance of carp—which Wayne described as a symptom of degraded environments—to the future of the breach in the brace leading to the paper mill. Carp he noted were very abundant in the Barwon but that by creating improved environments for native fish their survival prospects are much improved. Members asked whether the broken stonework on the race that leads to the Paper Mill should be repaired or replaced with a fish ladder. Wayne mentioned that this was a question that had been raised and that discussion of the topic will form part of the broader design considerations for the site.

Wayne generously remained for supper and members peppered him with questions.