The identity of the young plumber who drowned at a Mosman Park construction site last week has been revealed as Ryan William Duffus.

Workers on Wednesday afternoon tried desperately to pull the 26-year-old from a flooding trench, using a nearby pipe as a snorkel and screaming for help as he sank out of sight.

Harrowing details of the frenzied attempts to save the Bennett Springs man later emerged with nearby resident Robert Zammit telling Nine News Perth efforts to pull the worker out of the trench failed.

"It was traumatic to see these grown men screaming trying to get their friend out of the situation," he said.

"They were trying to pull him out of the water but it was quick sand.

"Within two minutes his head was under water, it was so quick everyone was doing everything they could."

Another witness, Alex, told Nine News Perth Mr Duffus was submerged in water up to his head when workers tried to help him breath with a nearby piece of pipe.

"One of [the workers] was almost submerged under the water - just his face with an open mouth - and the second [worker] tried to pull him really hard and was crying for help, crying not just screaming but crying," he said.

"Someone tried to find a pipe to give him like a snorkel.

"This guy was a real hero but unfortunately he wasn't helping his friend"

Desperate workers also reportedly used buckets and an excavator in their attempts to stop the water flooding into the two-by-one metre trench Mr Duffus was trapped in.

Initial witness reports suggest the incident was sparked by a burst water main.

Worksafe is investigating and police will prepare a report for the coroner.

Badge Construction chief executive Roger Zammit said the company was shattered by the incident which occurred on their site.