HOW long does it take about 100 million litres of water to fill a massive sinkhole? 

This hole at Darwin River was overflowing after about five hours last Friday. 

A timelapse video shows the sinkhole - which opened up in July 2014 - filling in a matter of seconds. 

Lance Hart owns the property and said the sinkhole was still underwater after almost a week. 

“It’s subsiding at the moment I can’t see the sinkhole it’s just a billabong now with an exceptionally deep water hole,” Mr Lance said. 

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“It’ll be interesting to see how long the water stays in the sinkhole.” 

media_camera Lance Hart with his backyard sinkhole when it first opened up in July 2014.  Picture: Helen Orr

Affectionately named Lake WTF, Mr Lance has accepted the lake into the family. 

“Once it became obvious that it was stable we went swimming in it.” 

“I’ve kayaked in it, swam in it,” he said. 

Mr Lance and his family regularly mount a camera on a tree to record the sinkhole to capture any changes. 

He said there had been no change following the few weeks after it formed in July. 

He mounted the camera on Friday predicting storms and rain due to the cyclone up north. 

Mr Lance said he noticed the rain get heavy from around 4am with the timelapse footage showing the hole rapidly fill up from 4am to 9am. 

media_camera After heavy rain the sinkhole has become an overflowing billabong, affectionately named Lake WTF.  Picture: Supplied

Mr Lance said his rain gauge recorded over 130ml during a 3 hour period from 4am. 

“It’s like the whole thing filled up in around five hours.” 

He said he was curious to see if the rain had changed the sinkhole. 

“I’m expecting it to have changed a little,” he said. 

It is estimated that around 50,000 cubic metres of dirt was sucked into the sinkhole when it formed. 

Mr Lance said he thinks that there is currently around 75-100 million litres of water in the sinkhole and the billabong bed it sits in.