Residents of Tsawwassen and the Gulf Islands have lost their bid to block plans for overhead high-voltage power lines through their communities as part of a new link between the Lower Mainland and Vancouver Island.

They've been lobbying for an alternative route. 

But the B.C. Utilities Commission says upgrading the power lines along the existing route is the most cost-effective way to meet future electricity needs on Vancouver Island.

That would take the line overhead from Ladner to Tsawwassen, then underwater to the Gulf Islands and then overhead again to Vancouver Island.

B.C. Transmission Corporation spokeswoman Donna McGeachie says the line is needed because demand for power on the Island is expected to grow by 50 per cent over the next 20 years.

"It's very important that we have a secure and reliable supply of power in place to meet the needs of residents and businesses on Vancouver Island," she said.

"We were very pleased the commission has approved this very important project."

The residents opposed to the project had argued that the overhead lines pose a potential threat to their health and to their safety.

Daria Zovi, who speaks for a group of Gulf Island residents, says the utilities commission seems to have dismissed all their concerns about the effects of electromagnetic fields.

"They haven't dealt with it," she said. "They said it doesn't determine [if] one project is better than the other."

But the utilities commission says it looked at the potential impact and concluded the risks are within the guidelines of international bodies such as the World Health Organization.