Wannon River Insights Part 7 — After the fire

It has taken more than six months to get there, but I have now had a decent look at the upper Wannon River following the summer bushfires. My greatest fear through this wait was that any significant rain would mobilise soil and ash, decimating the aquatic communities of the upper Wannon River. There has certainly been some rainfall events, but nothing extreme and certainly no signs of impending doom. What follows is a snapshot of what I have seen, and what I have learnt about this unique and precious waterway over the past few weeks.

My first foray back into the upper Wannon came in late June, The water was running clear and there were no signs of untoward impacts. I was initially concerned by the low pH (acidity) of the upper stream sections but after consulting the brains trust, and looking at historical data, this is pretty normal. For reference, rainfall is pretty acidic (pH = 5.6), owing to carbon dioxide in the atmosphere and the presence of carbonic acids. On top of that, the geology of the upper Wannon is characterised by silica rich, base poor sandstone (Siliceous Sandstone) and these substrates offer little in the way of chemical buffering. Iron and Aluminum mobilisation can act to further increase acidity, particularly when water first flushes the system after a dry period. There is also the potential for mobilised ash to contribute.

The images below show the places I visited, noting that on the days I visited the Wannon Creek diversion points, all of the flow was being intercepted (as shown) and sent north to Lake Bellfield, reducing downstream flows.

Another concern I had was understanding any flows that might have occurred in the catchment that we were not aware of, because of missing rainfall data in the months before the diversions started operating again in June. The Bureau of Meteorology’s Mt William weather station had been destroyed in the bushfire and was offline until early April 2025, causing a gap in rainfall data.

In its place, another weather station at Lake Bellfield recorded 42.2 mm of rainfall on February 2nd. This did not correspond with any immediate flow increases in the Wannon River at the Jimmy Creek gauging point, although there was a small pulse in mid-March. Indeed, flows didn’t really pick up until late July, following 58.2 mm of rain at Mt William on July 26th, with a total of 113 mm falling between then and the July 30th.

In summary, and given the exceptionally dry run we encountered in the first half of 2025, I’m confident that we haven’t overlooked any significant rainfall and flow events during the missing data phase.

Following the rainfall event in July, the upper Wannon River continues to flow clear, although a substantial proportion of the flow recorded in the Wannon at Jimmy Creek up until that point in time (942 ML of a total 2158 ML – or 44% of the total flow that could have been made available to the river above the Jimmy Creek gauging weir) had been diverted away from the Wannon catchment this year, and into Lake Bellfield (as explored further in this story).

The chart below shows the pattern of flows in mega-litres per day (dotted lines) at upstream flow gauging sites (https://data.water.vic.gov.au/WMIS) and also water depth in meters (solid line), further downstream at the top of the Wannon Fan (Lynchs Crossing).

You can see that diverted volumes (yellow dotted line) actually exceed the total river flow reaching the flow gauge downstream at Jimmy Creek campground, for a large proportion of the winter flow period to date, so the impact (the 44% reduction described above) is clearly significant. At the time of writing, flow data for the diversion outlet pipe is only available up until 29th July and does not capture the entire pulse following the large July rainfall event.

Beyond our interrogation of the available data, the real test of the bushfire impact is whether the true biological indicators (fish and crayfish) have held on.

During one of our reconnaissance visits, in conjunction with Glenelg Hopkins CMA staff, we walked a section of the Wannon River from Stockyard Creek, upstream to where the river meets the Grampians Tourist Road. We undertook some opportunistic dip-netting along the way and caught some juvenile blackfish and some Glenelg spiny freshwater crayfish.

This was good news because it is evidence that these susceptible species have so far survived having literally everything thrown at them – the dry conditions throughout summer, the fire, the failed autumn breaking rains, the ongoing diversion of the Wannon headwaters (from 1st June) and also any potential impacts following the fire. I’m hoping we can revisit the area for a more comprehensive survey later this year to better substantiate this.

In some further positive news, as of late July – and despite almost half of the Wannon River’s winter flow above Jimmy Creek being diverted, significantly delaying its arrival – the water has finally made it’s way through the Wannon Fan and is now filling Gooseneck and Brady Swamp,

I also had a chance to get a view of how the Wannon spreads out across the fan from the drone shot below. This is something we haven’t been able to see before, given it was obscured by the thick vegetation and tree canopy. The visit coincided with water just flowing into Gooseneck Swamp.

If you want to see just how slowly the water moves across this landscape, please also click on the video link at the end of this article.

So despite the catastrophic events of last summer, and the loss of 44% of the total flow volume (until late July) above Jimmy Creek during the operation of the diversions this year, the aquatic refuges of the Wannon River appear to have held on – at least for now.

The recovery of the wider floodplain relies on upstream flows. While these are making their way through, albeit at a rate delayed by the diversions, ongoing recovery will depend heavily on some nuanced thinking and responses from those responsible for managing the diversions, and giving the river (and its precious inhabitants) a seat at the table of resource benefactors. This will be required both in the short-term and as we go forward with the predicted and now realised impacts of climate change.

PS – you can read previous stories in our “Wannon River Insights” series here.