The giant Site C dam project has stopped construction of one road after a large 'tension crack' appeared on an unstable slope along the slide-prone Peace River banks near Fort St John.

'Significant' crack above Peace River

BC Hydro officials say the crack is 'significant' because it's almost half a kilometre long.

The utility made the information public Friday, six days after the crack was first discovered.

Officials say 30 workers on a road crew have been reassigned while the slope's safety is assessed by geotechnical experts.

Prep work for construction of the Site C dam takes place along the Peace River in 2016. According to BC Hydro, 2,357 people were employed by Site C in August, 2017. (Justin McElroy/CBC)

Road construction crew moved out

"No other work has been stopped," said David Conway, BC Hydro's community relations manager for the Site C project. "All other construction work is continuing.

Conway says the 400-metre-long crack or "stress fracture," is on the north bank of the Peace River, upstream of the dam construction site, near the Garbage Creek ravine outside Fort St. John.

The Peace River valley is an area prone to landslides.

"It's not unexpected," said Conway.

He noted that stabilizing the north bank of the river by removing soil is part of Site C's construction plan.

BC Hydro says crews have been excavating soil from the river bank area for 19 months to create 'stable slopes for dam construction.'

Geotechnical experts on site

Conway couldn't say how deep the fracture lies or whether it creates additional slide risks until the geotechnical investigation is done.

"I don't have that level of detail," said Conway. "The slope is stable. It's not moving. The crack is not growing."

About 1,500 workers have been at the $8.5 billion Site C dam project near Fort St John since construction began in 2015.

Once completed, the dam will flood a river valley 83 kilometres long and provide enough electricity to power the equivalent of about half a million homes.

The dam has been strongly opposed for years by environmentalists, local farmers and ranchers and some First Nations communities.