Actor Russell Crowe has thrown his weight behind a push to protect a north Queensland river on a wildlife reserve created to honour the late Steve Irwin.

In an interview during US prime time on the David Letterman show, Crowe said he was trying to save the area in memory of his friend, who died in 2006.

"He's not here to stand up for himself and I just feel, as his friend, that we can't do nothing," Crowe said.

"It is a global irresponsibility to do that.

"I made an offer to the Environment Minister [Peter Garrett] to have a talk about it, but he hasn't bothered to respond."

Crowe explained the Wenlock River operated as a water filter and was home to some unique plant and animal species.

His on-air plea saw more than 13,000 signatures added to an online petition for the "Save Steve's Place" campaign, taking the total number of signatures to 135,000.

A spokeswoman for the Irwin family's Australia Zoo said Steve's widow, Terri Irwin, and others associated with the fight were thankful for Crowe's support.

Cape Alumina has been conducting environmental studies on the site after winning a court battle to access about 15 per cent of the 135,000-hectare reserve.

The reserve on Queensland's Cape Yorke Peninsula was purchased by an Irwin family company, Silverback Properties, after Irwin's death.

Ms Irwin has strongly condemned the planned mine and says it will destroy a pristine environment, including the Wenlock River.

Cape Alumina chief executive officer Paul Messenger said while Crowe was entitled to an opinion, not all of what he said was correct.

"I think Steve Irwin had many friends and some of them are high-profile people who are entitled to their opinion," he said.

"But it is important to remember that we are not planning to mine the river or affect the river at all. We have no plans to mine any wetland areas."

Mr Messenger said Cape Alumina had permission to mine the land about three years prior to Ms Irwin being granted the reserve and said he expected operations to get underway in 2013.

- AAP

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