An employee of the NunatuKavut Community Council, which represents the Inuit-Metis of southern Labrador, said that council president Todd Russell was one of the people detained.
Tara McLean, Russell's executive assistant, says the protest continued Friday a short distance further down the highway.
Participants handed out pamphlets stating that the hydro project has proceeded without proper consultations or benefits for the aboriginal community.
Police say the protesters began blocking the road about 10 kilometres from the development at about 6 a.m.
The group has protested on the road before to express its opposition to the project on environmental grounds.
The $7.7-billion plan to create another dam on the Churchill River includes a new power station that would harness energy from the falls surrounded by the traditional hunting and trapping grounds of the Inuit and Metis.
The protest caused traffic to back up about one kilometre down the road.
The Mounties say it was peaceful, but protesters wouldn't co-operate with police, which led to the arrests.
The RCMP say the eight people arrested will be charged with obstructing a peace officer.
Nalcor Energy says the demonstration did stop workers from getting to its Muskrat Falls construction site, but operations at the project later returned to normal.
Energy from Muskrat Falls would be sent to Newfoundland and Nova Scotia using vast transmission lines and subsea cables.