Hopes of keeping one of Australia’s worst invasive species from breeding in Googong Dam, just outside Canberra, have been dashed after carp were confirmed to be breeding in the important drinking water reservoir.
The dam, which is located in New South Wales (NSW) near the town of Googong, is viewed by some anglers as a freshwater fishing oasis.
An ACT Parks website about recreational fishing in the reservoir still reads, “to date, carp have been able to be excluded”.
But an ACT government spokesperson has confirmed to Stateline that carp have been found in several parts of Googong Dam, which can hold 43 per cent of Canberra and Queanbeyan’s drinking water supply.
Sub-adult carp were also caught during surveys, indicating breeding has taken place.
Freshwater fish experts warn that if breeding is occurring then the population has established itself and carp may never be removed.
Associate Professor Mark Lintermans is a freshwater fish scientist at the University of Canberra with more than 40 years of experience and warned the species could boom over the next decade.
“If they are breeding, they are reproducing under their own steam and so a population will take off,” Professor Lintermans said.
“Control, given the current resources and tools we have, is virtually impossible.”
Although there have been carp sightings over the decades since it was completed in 1979, Googong Dam has been one of the rare reservoirs in the Murray-Darling Basin that has been considered mostly carp-free, helping boost its popularity with anglers.
It is estimated carp currently make up more than 80 to 90 per cent of the fish biomass in some waterways in south-east Australia and they are present in large numbers in Canberra’s major lakes.
“I’m not sure whether that will happen in Googong because you have a good native fish-stocking program there … but no, you can’t get rid of them,” Mr Lintermans said.
“You can’t fish them out, there’s talk about introducing a virus, but that’s still some time off.”
Reports from anglers sparked carp surveys
NSW’s fishing laws apply on the dam, however due to its role as a key drinking water storage facility, the ACT government manages the site and surrounding foreshore.
For several years now, its supposed carp-free status has seemed increasingly dubious.
There have been a number of suspected sightings and this summer a couple of fishermen have recorded videos of what appear to be carp swimming in shallow water.
“I was shocked to see them,” said local fisherman Paul Orman, who first saw carp in the dam three years ago.
“I didn’t think there were any carp in here and they kept telling me there are no carp but I said, ‘these are carp’. Probably about two months ago I saw another lot of carp.”
In response to written questions from the ABC, an ACT government spokesperson said “targeted electro fishing surveys” were carried out in late 2021, following “a report of carp sightings from a member of the public”.
Carp DNA had been detected in the catchment in 2019.
The surveys, which involved the NSW Department of Primary Industries (DPI) and utility company Icon Water, found both adult and subadult carp.
In response, the NSW DPI increased the stocking of Murray Cod and Golden Perch, predatory native fish, in an attempt to keep carp numbers low.
“Carp in high densities can impact water quality and water plants in the reservoir,” the ACT government spokesperson said.
“Once established in a waterway, pest fish (including carp) are extremely difficult to control. This is why it is critically important that people do not move live fish between waterways.”
A large female carp can produce a million eggs, which is one reason why the species is so invasive.
It isn’t currently illegal to immediately return carp to the water where they are caught but NSW DPI encourages recreational fishers not to do so.
“Carp in Googong are not in such high numbers to be a problem at present,” the ACT government spokesperson said.
“They are less likely to impact on native fish directly, particularly the stocked fishery of Googong that do not rely on fish breeding naturally.”
Googong Dam a ‘jewel’ in the crown of Canberra’s fishing scene
But anglers who regularly visit Googong Dam are disappointed and fear carp will eventually degrade the reservoir, like they have other places in the Murray-Darling Basin.
Rob Paxevanos, the host of Channel Nine and WIN TV’s Fishing Australia program, launched his career by catching giant Murray cod in the dam and said he was devastated.
“It was one of the last remaining freshwater systems that was carp-free, hence it was very clear,” he said.
“It’s a special place, an oasis, so close to Canberra.”
There are special rules designed to protect water quality at Googong because the reservoir is used for human consumption.
Swimming is prohibited and petrol boat motors can’t be used, while pets and camping are banned along the water’s edge.
Redfin perch, another invasive species which became established in the 1980s, and goldfish, are also caught in Googong.
“When carp breed to big numbers, they often result in murky water,” Mr Paxevanos said, reflecting on his experience fishing in the Murray-Darling Basin.
“The way they feed, they have a vacuum like mouth, they sift through the bottom, looking for bugs and vegetation and that process makes the water murky and it also removes the vegetation.”
“On top of that, they compete with native fish for their food and space.
“When the water quality gets low and our native fish are suffering, you’ll often see carp with their mouths out of the water, they can actually breathe air and survive.”
Carp could boom but won’t threaten Canberra’s drinking water
Mr Lintermans is not convinced yet that carp will make the water at Googong noticeably more turbid but he said anglers should brace for the possibility of the population growing rapidly over the next decade.
“I think they will [eventually] make up a substantial portion of fish in the dam,” he said.
“It will impact the fishery to some extent and so Googong, instead of being the jewel in the crown of the Canberra region will just be another good fishing spot.”
Googong Dam is just one of the sources of Canberra and Queanbeyan’s drinking water, which is provided to homes by the utility Icon Water.
Mr Lintermans said carp will not affect the quality of water that comes out of the taps of households.
It is fully treated with any taste, odour, pollutants and sediment removed.
“Icon Water utilise a multiple barrier approach to deliver safe, clean drinking water,” a spokesperson for the utility added.
To ensure the ACT’s long term water security during drought, a 12km long pipeline was completed in 2012 to transfer water between the Murrumbidgee River and the Googong reservoir.
It has several protection mechanisms to prevent the transfer of carp from the river to the dam and Mr Lintermans, who provided advice to the project, said it is highly unlikely to have been the source of the invasive fish population.
“There’s been odd records and sightings since about 1990 but we’ve always assumed they were stragglers that had been washed in or released as bait fish,” he said, adding that breeding is the key sign of an established population,” he said.
“I caught two in 1990, two large males, they couldn’t breed.”
Mr Lintermans said he suspected there were two possible sources of the current lot of carp.
He thinks they have either been washed in after heavy rain from a farm dam in the broader Googong catchment or that small carp have been used as live bait for Murray cod
“This has been coming for 40 years,” he added.
“Once they get in, they love a constant environment.
“Native fish are adapted to droughts and flooding rains — carp like it pretty constant, so they go well in reservoirs.”
Anglers want to help remove carp
Given the abundance of carp across the Murray-Darling Basin, some anglers want to be part of curbing the population of the invasive species, even if eradication is not possible yet.
“Carp make great bait for saltwater fish,” said Mr Paxevanos, whose TV show has loyal viewers and hundreds of thousands of social media followers.
“Maybe there’s a business out there for someone that the government can kickstart that can electro fish these carp en masse, or start to use them, or maybe the virus is the answer.
“Anything we can do to help the health of the waterway, anglers will just get behind it, there are millions of us.
“There’s a huge army of anglers that are mad keen to help once the government works out what the best approach is.”
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