Two B.C. First Nations suing one of the world's biggest mining companies over the fate of a northern river say a dam that Rio Tinto Alcan built 67 years ago reversed the river's flow, leading to a decline in salmon and sturgeon stocks and harming Indigenous communities.

The Saik'uz and Stellat'en First Nations were in court Monday to press their lawsuit against Rio Tinto Alcan, B.C., and Canada.

They contend that the dam, built to generate hydro power and smelt aluminum at Alcan's Kitimat plant, also reversed the river's course and diverted 70 per cent of the water flow for industrial use.

The First Nations say it's caused more than half a century of environmental degradation, harm to sturgeon and salmon, and damage to constitutionally protected Aboriginal rights.

"I'm the fourth generation of my family who's been fighting for the rights on the river. We want it restored," said Saik'uz band councillor Jasmine Thomas.

Saik'uz Coun. Jasmine Thomas, centre, joins other Indigenous leaders in playing a clan song on the steps of the Prince George courthouse. (Betsy Trumpener/CBC )

Stellat'en Chief Archie Patrick told CBC he wants Rio Tinto Alcan to dismantle the dam.

"They can take down the Kenney Dam and restore everything to the way it was in 1952," Patrick said on the steps of the Prince George courthouse.

"We're seeing it to the end."

'The Great River is Flowing'

The Nechako is a major tributary that flows into the Fraser River.

Thomas said in her Carrier language, Nechako means 'the great river is flowing."

But she says that's changed dramatically since the government granted Alcan a water licence, and the company built a dam that reversed the river's flow.

It's led to a sharp decline in salmon stocks. Sturgeon, a giant fish from the dinosaur era, is now an endangered species in the Nechako.

Rio Tinto Alcan uses the river water to power its aluminum smelter on B.C.'s north coast and to sell hydroelectric power.

Alcan created jobs

Its water diversion has created almost 2,000 jobs at its smelter, making it one of the biggest employers in northwest B.C.

Saik'uz elder Betsy William outside the Prince George courthouse, before she gave testimony in a lawsuit against Rio Tinto Alcan. (Betsy Trumpener/CBC)

A 200 day trial over the river's fate began in Vancouver in October in B.C. Supreme Court.

This week, court hearings moved to Prince George, so that local elders could give testimony and listen in on the proceedings.

On Monday morning, as nine black robed lawyers took their seats, seven Indigenous elders in full regalia smudged the judge's bench, waved spruce bows and sprinkled eagle feathers on the red carpet.

The elders told people in the packed court room that they were performing a cleansing ceremony.

Salmon 'all the time'

Betsy William, an 81-year-old elder from Saik'uz, was the first to take the witness stand. William described her family and nation's fishing practices before the Kenney Dam was built.

Flooding on the Nechako in 2007. Cheslatta Carrier Nation members blamed Rio Tinto Alcan, which controls water levels from the Kenney Dam. (Cheslatta Carrier Nation/Contributed )

"All the time — salmon," William told the court. " [You] just catch so much, it last til the next run."

The court hearings continue in Prince George this week, before returning to the Vancouver courthouse.

Rio Tinto Alcan said it won't comment while the matter is before the courts.

But communications and community manager Kevin Dobbin said the company has previously tried to resolve the matter directly with First Nations and prefers to settle the case out of court.

Dobbin also said Rio Tinto has always abided by all laws and requirements for using water and for protecting fish.