Bronte lifeguard Gavin Stevenson posted a photo of himself atop the marker on Instagram (@bagjuan) and Bondi Rescue Lifeguards shared his post to Facebook, where it caught the eyes of various Hawkesbury locals who found it to be a 'good humour story' in among the chaos from the floods.

"Hey Upper Colo (Hawkesbury), we've got your starboard marker. It's on the Lift at Bronte. We'd drop it to you but the 300kg train wheel attached to the thing is a bit too heavy and the 150km round trip sounds average," Mr Stevenson wrote in the post.

He told the Gazette that the starboard marker was found along with "so much" debris including "massive trees", some with "full branches still attached".

"Thankfully [the starboard marker] had a number on it and the guy who maintained it was able to tell me that it was commissioned at Upper Colo and that it was made from a 300-kilogram train wheel," he said.

He said he found it on The Lift at Bronte one morning when he arrived at work, and that it had since moved "a bit more up the beach" in the swell.

He said he wasn't concerned about it falling into the wrong hands.

"I don't think anyone can take it, maybe except a strong man!" he said.

A Transport for NSW spokesperson told the Gazette that recent rain and flood conditions have led to several of the state's navigation markers, including the green starboard marker which popped up at Bronte, being washed from their location.

"This will be retrieved and transported by truck back to its position in the Colo River," the spokesperson said.

"NSW Maritime has a 24/7 365 day arrangement with a contractor to manage the replacement of boating infrastructure.

"NSW Maritime predicts it may take weeks to complete a full audit of what is missing, order new infrastructure and have it installed.

"In the meantime, boaters are advised to use extra caution on the waterways, and keep lookout for debris in the water. Displaced navigation markers or hazards in the water can be reported on 1312 36 option 2."