Cataract Gorge missing swimmer - everything we know so far

Here is what we know so far:

Tasmania Police were first alerted to the missing woman about 1pm on Tuesday.

The woman in her 20s had been swimming in the First Basin when she became separated from her group.

The woman's friends and family alerted a nearby lifeguard by the pool. Shortly after, the police received a triple zero call.

As of Wednesday afternoon, the search effort has yet to find any sign of the missing woman.

A search effort was established by police on Tuesday and involved more than thirty people.

A Westpac rescue helicopter, a police drone, as well as police divers, SES volunteers and Surf Lifesaving volunteers were on site to assist in the search effort.

Launceston Surf Lifesaving Club president Geoff Lyons was among those assisting on Tuesday.

"We were called by the police to provide assistance and floodwater expertise," he said.

READ MORE: Meet the Northern Tasmanians receiving Australia Day honours

The combined search effort continued until 10pm on Tuesday night, at which point visibility became too low and a police presence was established overnight.

By Wednesday morning, the search effort had ramped up again and police divers arrived from Hobart to assist. There were seven divers on site with majority of the search's attention remaining on the First Basin.

Acting inspector Aleena Crack noted that the visibility underwater had presented a difficulty for divers, but that the lower water level on Wednesday would aid in the search effort.

While the water level at First Basin was higher than normal on Tuesday, Tasmania Police have not indicated whether the water conditions are suspected to have played a part in the woman's disappearance.

Hydro Tasmania, which regulates water-flow through the gorge, had scheduled a release from the Trevallyn Dam between 10am and 4pm on Tuesday. Another release was scheduled for Wednesday, but appears to have been held off to aid the investigation.

A Hydro Tasmania spokesperson said they had been contacted by Tasmania Police regarding the missing swimmer at Cataract Gorge and were supporting the search effort.

Police have cordoned off much of First Basin while the search is underway, but have not cut off the gorge to the public.

First Basin remains open to swimmers, indicating investigators are not currently concerned that the swimming hole presents a danger to public safety. That said, police are continuing to ask the public to avoid the area while the search is underway.

Both Cataract Gorge cafes and the chairlift remain open to the public, as do many of the walking trails.

Rising flood waters and choppy conditions at First Basin have caused issues for swimmers in the past. Earlier this month, a man was rescued from Cataract Gorge amid fast-rising floodwaters.

In 2011, a flash flood caught swimmers Dylan Beardsley and his girlfriend unawares and led to them being evacuated from the water via a rescue helicopter.

As noted before, however, it remains unclear if the water conditions at Cataract Gorge on Tuesday are related to the woman's disappearance.