THE Collie Shire Council’s spraying program of water plant nardoo during the past 12 months has achieved excellent results according to local river expert Ed Riley.
The plant had been growing out of control due to an increase in nutrients in the water.
Apart from being unsightly, the plant also removed oxygen from the water, potentially suffocating aquatic life in the river.
An eight-kilometre stretch of the river has been identified for treatment with a particular focus on a 900-metre section of the river.
The section – downstream from Paterson Street bridge to the eighth fairway at the Collie Golf Club, with treatment finishing at the Number 2 pump – was treated first to minimise any adverse effects on the environment.
Initial treatments of the weed were disappointing until the Reglone/Hydrogel mix was sorted out.
When correctly applied the chemical effect on the nardoo was obvious and within a couple of days there were visible sign of the plant turning brown.
Some regrowth has occurred but it is expected to be treated easily. Mr Riley said there had been minimal evidence of any unintended impact of the weed treatments.
“After spraying commenced, there was a noticeable decline in water fowl numbers that grazed on nardoo and to a lesser extent also the coote and dabchick,” he said.
“Their relocation was only temporary with numbers now returning to normal while several swans have been seen feeding in the area over a six week period.”
Early in the treatment process there was also concern with the large amount of dead dragonflies in water and the disappearance of molluscs from two locations within the trial area.
There was also anecdotal evidence from a fisherman who said he caught numerous smelly cobbler of unusual colours.
It was also noted that marron numbers had been disappointing and there had been no sightings of water rats.
Mr Riley said after not fishing in the area for a time, river bank monitoring only revealed one dead perch.
“Following on I examined dozens of redfin of all sizes including stomach content; they were in good condition and acceptable colour but I noticed a distinct lack of crustacean in their diet,” he said.
“The dominance of cobbler is of concern, something appears out of balance.
“There have not been many freshwater shrimp at the site or downstream.”
Despite urging from some prominent people to spray all the nardoo in one go, the Collie Shire and regulatory bodies stood firm, a decision Mr Riley believed was the right call.
“It would have been a totally irresponsible environmental disaster if some had their way (spraying all the nardoo at once),” he said.
“There would have been hundreds of tonnes of liberated rotting material, plummeting oxygen levels, flyblown weed for the river to contend with and daily mine water discharge of around 5mg of consequence.”
Mr Riley said continued monitoring and research was needed after any trial or application of chemicals around the river.
The Collie Shire’s consultant last visited Collie in May last year and April this year.
Another cause for concern was the recent prevalence of green algae in formerly pristine creeks and the Collie River over the past 20 years.
“As an example, the recently established green algae is the river bed below the new Coolangatta gauging station,” Mr Riley said.
“Despite ongoing research, no one seems to want to know about what the future holds for the Collie River.
“One thing is for sure when the benefits of the coal mine water discharge cease, a new source of water will have to be found to water Collie’s parks, gardens sporting grounds and golf clubs as the river will become too salty to use.
“The Collie Shire’s recent decision to broaden the scope of the Weeds and Waterways Advisory Committee was long overdue.”
