Q: How healthy is the Merri?

Q: How healthy is the Merri?
A: Ask the water-bugs

For many years, Julia Cirillo, of the Merri Creek Management Committee, ably assisted by Trevor Hausler, has conducted community education programs about the importance of water bugs – aquatic macroinvertebrates – to the ecology of the Merri Creek.

On 19 April 2026, Julia and Trevor delivered one such program on the Creek at the end of Lorne Street, Fawkner.

Image credit: Heather Harris, of the Merri Paddle, explains the work of The Paddle.

The event was co-sponsored by the FoMC Merri Paddle, the working group of Friends of Merri Creek dedicated to improving the aquatic ecology of the Creek, with the long-term aim of returning the platypus to the Merri.

Why water bugs? Because they sit at the centre of the Creek’s food chain — essential for platypus — and because their diversity provides a reliable measure of ecological health. 

Participants entered the creek with nets, sampling riffles and edges, then returned to sort their catch into trays. At first, what looks like debris quickly resolves into a living system: caddis larvae, beetles and a handful of more tolerant species.

Image credit: Gathering samples.

Image credit: Dragonfly nymphs.

The results are translated into a SIGNAL score (Stream Invertebrate Grade Number – Average Level), which rates water quality based on how sensitive the species present are to pollution. Sensitive species lift the score. Tolerant ones drag it down. A score of 6 and above indicates a healthy ecosystem.

At Lorne Street, the result was sobering. A SIGNAL score of 3.9 (weighted 3.6), with just 14 taxa recorded, indicates a waterway that is heavily impacted.

That finding reflects two persistent pressures on the Merri:

• pollution, carried in stormwater as sediments, nutrients and contaminants; and
• unnatural flow patterns, the defining feature of urban stream syndrome.

Urban stream syndrome describes what happens when a catchment is progressively built over. Rain that once soaked into soils and wetlands is instead captured by hard surfaces and drains, then delivered rapidly to the creek. The result is a system of extremes: short, erosive bursts of high flow after rain, followed by low flows in dry periods. Habitat becomes unstable, sediments are mobilised and ecological diversity declines.

For water bugs, this means fewer species and a shift toward those that can tolerate degraded conditions. For the Creek, it means a system under stress. For the platypus, it means an inadequate food supply. The key point is that these pressures begin upstream. The condition recorded at Lorne Street is not created there. It is the cumulative effect of what happens across the catchment.

That is why attention is increasingly turning to the upper Merri and the proposal for the wallan wallan Regional Parkland.

Before colonisation, the upper catchment was a wonderland of seasonal wetlands — slowing water, filtering sediments and supporting biodiversity. Much has been lost, but important remnants remain. These systems act as the natural kidneys of the creek, moderating flows and improving water quality.

The proposed regional park represents perhaps the last opportunity to protect and restore these functions at scale. If secured, it would help reduce the very pressures now seen downstream. It would moderate runoff, improve water quality, and rebuild ecological resilience.

In that sense, the lesson from the day is clear. The Merri is not beyond recovery. The presence of 14 taxa shows there is still life in the system. Reversing the impacts of urban stream syndrome will require action at the scale of the catchment, not just the channel.

The water bugs tell us how the Creek is functioning today. The regional park is about whether we can change that story.

The work of the Merri Paddle has been made possible through the support of Friends of Merri Creek and a number of local Rotary clubs — Pascoe Vale, Coburg, Moreland and Preston — together with a Rotary District Grant.
Their contributions have enabled community programs that build both understanding and capacity to care for the Merri – if you’d like to get involved with the Paddle, reach out to friendsofmerricreek@gmail.com

Image credits: All photos by Julia Cirillo, MCMC.