Wetland thriving with aquatic life again a glimpse of carp-free future

The Murray River looks magnificent as it meanders past Limestone Cliffs and towering red gums but there was once a time when the waters ran clear. 

A dwindling number of locals still remember when you could see through the water to a biodiverse world below. 

But then came the explosion of carp and other environmental disasters.

At Teal Flat Hut wetland though, things are looking a little bit different.

The afternoon Sun is high as Murraylands and Riverland Landscape board ecologist Amy Rice and team leader Darren Willis gear up to wade into the wetland.

As the pair push through lush aquatic plants, they may as well be travelling back in time, to an era before an invasion of carp changed Australia's largest river system.

Species sanctuary

The lagoon, an hour-and-half drive from Adelaide in South Australia's Mid Murray, is one of 25 pool-connected wetland sites managed by the Landscape Board's wetland team. 

The rich habitat at Teal Flat is achieved by closing the wetland to the river and allowing it to dry out through evaporation, which kills the carp. 

When the wetland is refilled with river water, carp screens are used to exclude the fish.

"When you come out and have a look at a wetland like this, it never ceases to blow you away,"

Mr Willis said.

Ms Rice said the environment was reaping the rewards.

"We've got an amazing array of aquatic vegetation from ribbon weed to red water milfoil, which are supporting an array of different species, from fish to birds to frogs to turtles," she said. 

"We've got lots of small-bodied native fish utilising the wetland and the different functional groups of birds that are utilising it, such as swans, which are herbivores, to musk ducks, which are piscivores, so they're eating those small fish in there."

Ms Rice dips her turbidity meter below the crystal-clear surface of the wetland. Her reading reveals a very different story to the "mocha coffee brown" Murray River just across the bank.

Mr Willis explains that the difference is due to the large numbers of carp stirring up the river with their "mumble" feeding. 

Carp have altered the biodiversity of the Murray-Darling Basin, with the federal government listing the Murray River, flood plains and wetlands downstream of the Darling River as critically endangered.

Multiple threats have led to the listing by the Threatened Species Scientific Committee, including reductions in biodiversity and conditions that favour invasive species, like carp.  

"They're what they call ecosystem engineering species," Mr Willis said.

"They suck up the soil off the bottom, squirt it out through their gills, which mobilises in the water column, and keeps the water really murky.

"It's just that inability to photosynthesise that suppresses all of the plant vegetation."

Carp complacency

Since 2016 the federal government has spent more than $10 million researching a carp herpes virus as a biological control method, with further research due by 2028.

In the interim, fishers and conservationists are pushing for more carp management, with an action summit held in Victoria earlier this year.

Summit organiser Victorian Fisheries Authority has since launched a carp action alliance, with senior fisheries manager Anthony Forster calling for trials of the carp herpes virus to be released in enclosed waterways.

"There's a real sense of frustration but also a real sense of optimism about what we can do together,"

he said.

Clear comparison

Charles Sturt University fisheries researcher Ivor Stuart, who also attended the forum, said it was critical to take action now, especially with reviews into the Murray-Darling Basin Plan and Menindee Lakes due to report back later this year.

But he acknowledged a sense of complacency makes it hard to get traction.

"I'm part of the carp generation," Dr Stuart said. 

"I've never seen the river looking anything other than carpy, and discoloured and degraded."

In South Australia, where the river is regarded as critically endangered, Renmark resident Brenton Beal remembers how it looked before it was filled with carp.

"The water was much clearer back in the '60s. We caught redfin, callop, the odd cod, certainly there was no carp back in them days," he said.

"You could see down possibly nearly a metre in the water, see the propeller on your boat turning, see fish swimming."

Beyond the virus

Back at Teal Flat, Mr Willis says the Landscape Board's carp exclusion could be a blueprint for other regions to revitalise their waterways.

"There's a lot of interest in the upstream states in looking at the case studies we have here and seeing how they can be applied at different scales upstream," he said.

For now, the wetland provides a glimmer of hope into what could be possible, even without a carp herpes virus.  

"I think it is definitely hard and a labour of love," Ms Rice said.

"It's that common goal of we want to make a habitat and an environment … that's able to provide a safe haven for these native species that we want to see in the system for a long time."

Watch ABC TV's Landline at 12:30pm on Sunday or on ABC iview.