Intense heavy rainfall in parts of Western NSW has triggered a massive fish kill near Dubbo and sparked renewed calls for action to be taken to stop a staggering decline in the native fish population.
Downpours last week increased flows into the Little River and stirred dirt, sediment and rubbish which severely reduced oxygen levels in the Macquarie River. It made a significant area within it uninhabitable for thousands of fish.
A 32-kilometre stretch of the river was affected and Inland Waterways president Matt Hansen said he had never seen a fish kill like it in his lifetime.
"To watch the baby catfish driving themselves up the beach and gasping for air, it was a very sick river over the weekend," Mr Hansen said.
"Everything came to the top and you could see the carp with their lips out of the water, gasping for oxygen.It was an incredible sight to see and one I hope I'll never see again.
"The cause of this event is a massive, massive influx of sediment and turbidity in the water which has crashed the dissolved oxygen levels."
Mr Hansen said oxygen levels needed to be between four and 15 milligrams per litre for fish to be healthy.
"We've seen crashed dissolved oxygen levels to 25 per cent of what they should be, 0.16 was one read," he said.
"It's inevitable that we were going to see these events happen but now more than ever our native fish need a hand from us to recover.
"We need to open fish passage downstream of Dubbo at the North Dubbo Weir and the Gin Gin Weir.
"Some of our best fish breeding sites are downstream of Dubbo and in a normal environment you would see breeding events occur and fish naturally move up and repopulate areas that have had fish kills like this.
"Sadly our river is sick in more ways than one and we've made some of those illnesses ourselves by blocking fish passage. We need fishways on the Gin Gin Weir and the North Dubbo Weir as soon as we possibly can to see our fish recover."
Authority is acting
Senior NSW Department of Primary Industries (DPI) Fisheries manager Sam Davis said the organisation anticipated "events like this" and urged the public to report fish kills.
"When the river and the catchment starts to recover after rainfall events, that will have impacts on water quality and in this instance it was a sediment-based impact," Ms Davis said.
"It's quite important that we keep noting these events because that will help in us putting resources towards recovery actions.
"DPI Fisheries have committed extra $10 million to addressing the drought impact on native fish."
Ms Davis said the DPI had upgraded hatcheries and facilities to house an "insurance population" of fish.
"These are our big breeders who we are going to need when times get better to repopulate the river."
According to Ms Davis, conditions this summer have been "unprecedented" and the magnitute of the Dubbo region fish kill was "quite significant".
"Throughout this summer it has been an unprecedented scenario for the department, in terms of the pressures that are on our native fish," she said.
"Yes fish kills do occur in history, but unfortunately fish in the past have not been subjected to the pressures we've got today. Within the past 200 years, since European settlement, we've introduced a whole heap of pressures our fish haven't been subjected to.
"The magnitude of this kill is quite large...it extends from the confluence of the Little River with the Macquarie, all the way down to Dubbo."
Conditions still bad
More fish kills should be expected, Ms Davis said.
"I've been looking downstream and talking to rec fishers and farmers and they haven't seen any fish kills yet. However the water quality is very ordinary, the dissolved oxygen is very low."
"We need to manage our river corridors sensitively and make sure that we have the right plant and tree species because they provide the food sources fish need and they provide the snags which are the coral reefs of our inland rivers.
"We need to allow fish to move so they can breed and access their environments.
"We need to look at what's happening with our fish in terms of being drawn out of the river, so screening pumps and those sorts of things so we keep fish in the river where they belong."
Mr Hansen agreed more needed to be done to keep fish in rivers so population numbers would be higher in the face of weather events that lead to fish kills.
"Research shows that in the Murray Darling Basin we remove millions upon millions of fish every year, up our irrigation pipes because they're not protected," he claimed.
"Australia is well behind the eight ball. We've got some trials and stuff starting to happen and slowly fish screening is starting to become accepted and appreciated.
"It's not something new, in the United States they've been protecting their fish stocks for over 100 years with fish screens on pumps.
"In NSW alone we stock two to three million fish and it's estimated we suck 90 million out...up into the irrigation channels, up the sprinklers, into the on-farm storage, never to be returned to the system.
"We can do much better for our fish than what we are."
Mr Hansen said he believed native stocks had "crashed by 70 to 90 per cent since European settlement".
"Just in 200 years we've absolutely smashed them," he said.
"We're certainly going to need some government intervention to get the right infrastructure in place on those barriers to fish passage and also our off-take in irrigation pumps.
"Restocking is a band-aid solution...naturally and having fish do it on their own is the most cost effective way to do it.
"Fingerlings are extremely dear to produce but if you can get these beautiful big breeders doing it on their own in the river that's the way forward for the most healthy river we can have.
"We need to open those breeding grounds up for us now more than ever or we're gonna have nothing up here."
Without more government intervention, Mr Hansen said he feared the environment and economy would suffer.
"We will see a decline in fishing tourism and we'll also see local businesses affected - camping stores, fishing stories - who all rely on the fantastic fishing that Dubbo has been renowned for."
Councils to clean up
Ms Davis said local councils were largely responsible for the clean up in the wake of fish kills.
"In the instances where there's likely to be a significant health issue in a high settlement area or a high recreation area the responsibility is with the local council, however with significant kills DPI Fisheries have been giving assistance... so we can get the job done quality and provide assistance to councils," she said.