River threat removed – at least for now

A CLEAN-up of an aquatic fern outbreak at a refuge pool in the Moorabool River has averted what could possibly have been a disaster for the waterway, according to one of its organisers.

Cameron Steele, who coordinates People for A Living Moorabool (PALM), said the effort by 10 people earlier this month to combat an outbreak of Azolla – a floating fern often mistaken for algae – had been successful.

 

But he said if he and others had not intervened, the result could have been devastating for the river.

“If we hadn’t done it that pool would have gone anoxic (a complete absence of oxygen) and migratory species like fish, that pool becomes quite toxic to them,” Mr Steele said.

“What we’ve done is given the river a chance to get through summer without a really adverse impact at this particular site.”

PALM and members of the Geelong Underwater Hockey Club spent a day raking and removing the Azolla and depositing it on the banks.

The outbreak happened earlier this year and covered one of the half-dozen refuge pools along the river in what is thought to have been the worst infestation in 20 years.

 

“It’s normally found in still water, so to have it cover that particular refuge pool was an indication of how poor the water flow has been in the river,” Mr Steele said.

“The Moorabool is regarded as the most flow-stressed in the state, so it was a real wake-up [call].”

Mr Steele said the outbreak had refused to budge throughout winter, even though it was at this time of year – as nutrient levels peak and water temperatures rise – that infestations normally start to disperse.

 

But this year the Azolla did not disperse, he said, and when it died it could drastically reduce oxygen in the water and lead to fish kills.

“We felt it was pretty urgent that we tried to deal with it before we marched into summer,” Mr Steele said.

He said native river reeds had clearly been affected but were now starting to regain some of their colour, and fish species were also back in the pool.

“Hopefully this is a one-off and not a sign of things to come,” Mr Steele said.

“It’s very concerning for the river, and it will take us really keeping an eye on the waterway [to prevent a recurrence].”

Mr Steele said the outbreak had needed “a substantial flush” to get it out of the pool.

 

“And we didn’t see one over winter, it just never happened,” he said, adding that rain during spring also had not contributed enough to river flow.

“We felt that the likelihood of it sticking around, right into the heat of summer and the low flows of summer, was very, very real.”

The affected pool is about 600 to 700 metres downstream from the Batesford Hotel, and parts of it are as deep as 3.5 metres.

“Rivers talk to you in various ways, and this one was basically saying ‘Hey, I’m in strife’,” Mr Steele said.