Environmental activist Bob Brown says his planned road convoy to protest the proposed giant Adani coal mine in Queensland will be bigger than the protest to stop the damming of Tasmania's wild rivers in the 1980s.

His foundation's "Stop Adani Convoy" plans to travel from Hobart to the coal port of Bowen on the Queensland coast over a fortnight starting from April 17, Mr Brown told the Herald.

Bob Brown predicts his 'Stop Adani Convoy' will be bigger than the campaign to save the Franklin River from being dammed in the 1980s. Credit:Peter Mathew

The ferry and road trip has lured more than 800 participants, a number that Mr Brown expects to swell as the convoy snakes through Melbourne, Sydney and Brisbane on its way north.

"We're very, very anxious" about recent announcements that work on the long-proposed Carmichael mine in the Galilee Basin is about to begin. "The option of doing nothing is not on."