Former Australian Greens senator Lee Rhiannon has pleaded guilty for her involvement in an angry protest against a bridge development in north-west Sydney earlier this year.

Ms Rhiannon and two men — Paul Evans and Michael Eggleton — were charged with minor offences after the protest against the Windsor Bridge redevelopment turned violent in January.

Dozens of angry local residents linked arms and were preventing a truck from entering a work site when they were told to move on by police.

The protestors refused, which led to pushing and shoving with officers and eventually the arrests.

Archaeological survey works were taking place at the site at the time, examining a barrel drain which runs through the site — which was built in the 1800s.

Local resident believe the drain holds special significance because of its age and association with the town of Windsor, which is one of five 'Macquarie Towns' — or settlements created by governor Lachlan Macquarie during early European settlement in Australia.

They fear the redevelopment of the nearby Windsor Bridge will damage the heritage of the area and have been protesting against it for more than five years.

Ms Rhiannon, Mr Evans, and Mr Eggleton all pleaded guilty to their charges in Parramatta Local Court today.

Magistrate Theo Tsavdaridis noted the importance of protest in democracy.

"It seems to me … all [protestors and police] were in some way justified to do what it was they were doing that day," he told the court.

"I can understand that there are residents concerned about the trashing of something which is to them a site of cultural significance."

Mr Evans and Mr Eggleton were placed on six-month good behaviour bonds with no convictions recorded.

Ms Rhiannon, who retired from the Senate last month, had no conviction recorded and was not further punished.

The protest at the site of the Windsor Bridge redevelopment continues.