The fight to save Tasmania's Franklin River from damming, and damning, in the early 1980s proves a fascinating insight into that era's social and political turbulence in Kasimir Burgess's moving and marvellous documentary.

More than an archival footage jigsaw puzzle or a talking-head interview film, although it is also both of those things, what draws the audience along on this film's adventure is the current-day story that carries its narrative.

Burgess's camera team follow young Oliver Cassidy on a rafting trip down the Franklin River, an arduous and dangerous physical journey, but also a journey of insight for Oliver.

While Oliver keeps his own written journal of his current-day rafting expedition, we hear the writings Oliver's father made on a similar journey decades earlier, Oliver's father being Mike Cassidy, a contemporary of Bob Brown and one of the early instigators of the movement to stop the construction of the proposed hydro-electric dam that would drown much of the beautiful country and biota of his beloved Franklin River.

Oliver was barely a week old when his dad embarked on this same week-long rafting journey down the Franklin, to join a blockade attempting to halt construction works, and where he would be arrested.

As Oliver, and cinematographer Benjamin Bryan, make their way through the pristine riverine and rainforest landscapes, Burgess and her co-editor Johanna Scott weave in the story of the fight to save the Franklin, beginning with Oliver's recollections of his father, and moving to those talking-head interviews, and plenty of archival footage.

But what a tale that fight was, and while it was years in the making, this film's tight 91-minute runtime make it a short and fascinating exercise in unpacking the tactics at play on both sides of the ideological fight - environment over jobs and development.

Today's young folks are brought up understanding marketing and media manipulation, but for young Tasmanian doctor Bob Brown and his contemporaries, it was all "necessity is the mother of invention".

In an interview, Bob Brown discusses their unexpected luck at drawing international media figures like the British naturalist and television identity David Belamy to their cause, and how their recruitment of photographer Peter Dombrovskis, whose photo of Rock Island Bend - one of the spectacular areas that would have gone underwater should the dam have progressed - became one of the media touchpoints of the campaign.

There's a handful of upsetting moments in this doco, notably the recollections and footage of damage done to a tree, one of Australia's oldest and pre-dating the era of Jesus Christ, that some angry pro-dam campaigners destroyed in an act of retaliation when works on the dam were ceased.

There are also many scenes of great beauty - Benjamin Bryan's camera takes us places most of us will never see except in films like this.

And coming back to Oliver's story, much more than documenting this young man's personal journey building an understanding of the motivations and passions of his late activist father, it's a journey for this young man redefining his physicality - when he takes his shirt off in the river we see the tape from his recent top surgery - a trans man learning from the journals and actions of his late father what it means to be a man.

What a fearless bunch of people were the contemporaries of Oliver's dad Michael. While Bob Brown went on to national politics, many were just ordinary men and women prepared to be jailed for their protesting and activism.

Burgess's interviews aren't one-sided, and there's plenty of reflectiveness from folk on the other side of the fight.

The MA rating on this film is a little surprising and don't let it put you off. It stems from the name-calling and other foul language thrown between the greenies and their opponents in the archival footage, along with a few inappropriately-worded placards.