For decades, anglers would visit Lake Sorell in Tasmania's central highlands in pursuit of wild brown trout — the prized catch that has drawn fishers to the region since the 1800s, when the species was first introduced.

Key points: Authorities thought they had won the battle against carp in 2009, but were mistaken

Authorities thought they had won the battle against carp in 2009, but were mistaken A second round of measures have reaped rewards, with the waterway set to reopen to trout fishing for the first time in 25 years

A second round of measures have reaped rewards, with the waterway set to reopen to trout fishing for the first time in 25 years Whatever remaining carp are swimming in the lakes, it is thought many of the males have "jelly gonad disease"

"We were pulling four-pound fish out of Lake Sorell every time we'd go out fishing," Cheryl Williams, treasurer of Bridgewater Anglers Association, said.

"A lot of people will tell you that they bagged out every time they came fishing here, it was so popular."

But that was before European carp, the dreaded invasive species which reduces water quality, degrades riverbanks and increases erosion, was found to be in Lake Sorell and neighbouring Lake Crescent in 1995.

The official number of carp taken from the lake system has been put at 41,496. ( Supplied: IFS Carp Management Program )

The closure of the waterway, to prevent carp spreading and causing the sort of destruction seen throughout the Murray Darling Basin system, was a blow to Tasmania's angling community — but the long wait for the trout fishing faithful is about to be over, with Lake Sorell opening up for the remainder of the season, this weekend.

Jonah Yick says after years of work, the catching of a single carp causes "excitement". ( ABC News: Mitchell Woolnough )

But it has not come easily, with authorities being caught out once before, when after months of work and tens of thousands of carp captured, Lake Crescent was declared "carp free" in 2009 — only for the fish to spawn in Lake Sorell the same year.

"We were down to the last 50 carp, we think," Jonah Yick, Inland Fisheries Service Carp Management Program lead, said of the first attempt.

"Unfortunately, there was a large spawning and resulted in about 50,000 juveniles."

Undeterred, the team redoubled their efforts — with new technology proving to be a game changer.

"There was a lot of information from the mainland of Australia on carp management, but no one had ever really taken on something of this size as an eradication program," fisheries officer Chris Wisniewski said.

The tactics of the previous campaign were repeated, with barriers put in place to prevent the carp spreading downstream into one of Tasmania's largest river systems, the Derwent.

But this time, male carp were implanted with GPS trackers to discover preferred spawning habitats, with the fisheries team concentrating their netting in those areas.

Authorities say they are confident the carp population at Lake Sorell won't rebound as it did in 2009. ( ABC News: Mitch Woolnough )

Thousands of fish were removed from the 74-square-km waterway.

"I think our best day was 750 carp in a single day, back in 2012," Mr Yick said, with the challenge then becoming the need to stay disciplined as the population plummeted.

"This season (2019/2020) I think we've caught four carp in five months, so we spend a lot of hours and a lot of days pulling nets for nothing."

"Now, the excitement is all around one carp," he said.

'Jelly gonad' disease set to finish off stragglers

With the official number of carp taken from the lake system at 41,496, the Inland Fisheries Service has stopped short of declaring the pest completely eradicated.

While there may be a handful of fish remaining in the murky waters, it is believed 50 per cent of the males have hypogonadism — sometimes referred to as "jelly gonad" disease — due to inbreeding, rendering them infertile.

Carp caught over summer were found to be stunted, with females still with their eggs, evidence they had not spawned.

After 25 years, Lake Sorell will reopen to the public. ( ABC News: Mitchell Woolnough )

Guy Barnett, Minister for Primary Industries and Water, paid tribute to the team.

"This is a fantastic milestone for the carp management program and a testament to the dedication, determination and resolve of the staff," he said in a statement.

"I look forward with anticipation to the confirmed eradication of carp from Tasmania over the next few years."

While the Inland Fisheries Service team is confident the carp population won't rebound as it did in 2009, they plan to monitor the lakes, working alongside anglers.

One of those keen to get back to the lake system is Cheryl Williams.

"I think we'll be flooded with fishermen here initially. It will take a while for the lake to recover to the fishing conditions that we've enjoyed in the past," she said.

"I think we are all anxious to get back out there in our boats and see what's going on."

Lake Sorell reopens to the public from Saturday, February 8 for the remainder of the 2019-20 brown trout season, which closes May 3.