As many as 1000 trees along the Cooks River are being assessed for potential removal by energy companies, which operate an underground network of pipelines running beneath kilometres of parklands in south-western Sydney.

Hundreds of mature trees – including Moreton Bay figs, eucalypts, and casuarinas – which line kilometres of pipeline easement from Port Botany to Newington in Sydney's inner west have been tagged by arborists to determine whether they pose a threat to the pipelines.

As many as 1000 trees along the Cooks River are being assessed for potential removal by energy companies. Credit:Paul Miller

"No one was notified, it just came out of the blue," said Peter Munro, the secretary of Cooks River Valley Association, which has been monitoring the river since the 1920s.

He said a volunteer first noticed the metal tags in June. They were attached to trees he had planted during the 1970s as part of efforts to regenerate the area after the pipelines were laid.