It's a new and permanent piece of street art in south-west Victoria that came about by happy accident.

The hugely popular drawing on a railway bridge in Warrnambool shows a wombat seemingly emerging from a hole in the bridge.

Artist Jimmi Buscombe said the artwork, which took about three hours to complete, was intended to be a test run that would wash off in the rain.

"I'd been hired by Warrnambool City Council to do a piece done in pastels and I needed to have a bit of a practice, so I snuck down to the bridge that's literally at the end of my driveway outside my house," he said.

"I probably should have got permission but I thought 'I'll just go have an experiment — it's only chalk, it's gonna last a couple of days, if it rains it'll come straight off'."

Artist Jimmi Buscombe and former graffiti removalist Phil Hoy. ( ABC South West Victoria: Matt Neal )

The wombat immediately drew a positive response from passers-by, so Mr Buscombe decided to leave the artwork up over the weekend before returning to wash it off.

Enter former graffiti removalist and local larrikin Phil Hoy, who lives nearby.

"I was out the front mowing the nature strip and I could see a bit of attention on the other side of the bridge of people looking and taking photos so I thought 'well, there's something going on'.

"So I went and had a squiz and then once I saw what I saw I thought 'yeah, this is [awesome]'.

"I thought 'well, someone around here has got talent'."

Realising the drawing would wash away in rain, Mr Hoy put on a high-visibility vest and grabbed a spray can of automotive clear coat.

"I thought 'well, it's gonna rain and it'll be gone'," he said.

"It needed saving. It can't go."

Warrnambool's Phil Hoy decided the wombat mural needed to stay, and so took it upon himself to make that happen. ( ABC South West Victoria: Emily Bissland )

So when Mr Buscombe returned a day later to scrub it off, he realised something was wrong.

"As I walked up to it I noticed it was shiny and I thought 'oh my god — it looks like it's had some chemical reaction'," the artist said.

"I rub it with my finger and it's not coming off and I dip my cloth in and I'm starting to wipe, and it's just not moving.

"I start to panic. I was freaking out a lot because you can get in a lot of trouble — I mean, it's essentially graffiti."

Word eventually got back to Mr Buscombe that Mr Hoy was responsible for "saving" his artwork from being washed away, so Mr Buscombe paid him a visit. He said he now found the whole thing "hilarious".

"I chatted to him for about half an hour and then it turned out that at one point in his career he was the contractor as the graffiti removalist for Warrnambool City Council, and here he was protecting my graffiti with a clear coat," Mr Buscombe laughed.

The mural was covered with an automotive clear coat. ( ABC South West Victoria: Matt Neal )

The situation has since been explained to Warrnambool City Council, who are happy for the artwork to remain, perhaps proving the adage about it being easier to get forgiveness than permission.

The story has certainly tickled the public, with hundreds of thousands of people having watched a viral video of the artwork.