FREDERICTON -- For the past 45 years, the Mactaquac Hydroelectric Dam has been a reliable and clean source of power in New Brunswick, but faulty concrete is forcing NB Power to decide its future well ahead of the century it was expected to last.

NB Power president Gaetan Thomas says studies and public consultation will have to begin in the next year if a decision on the future of the 653-megawatt facility is to be made by 2020.

"We are very keen to establish a full dialogue with New Brunswickers," Thomas said in a recent interview.

"Mactaquac is a large portion of our renewable energy for the province of New Brunswick."

In fact, the dam produces enough electricity to meet about 20 per cent of the province's energy needs.

Located about 15 kilometres west of Fredericton, the dam is topped by a two-lane highway connecting the communities of Kingsclear and Keswick Ridge on either side of the St. John River.

When construction began in 1966, families were displaced as communities and farmland upriver were flooded, creating the headpond above the dam.

While the actual dam is constructed of rock and clay, the concrete used to construct the spillways and generating station suffers from a condition known as alkali-aggregate reaction, which causes the concrete to expand.

Thomas said the condition is common at hundreds of dams around the world and requires ongoing maintenance.

He said the utility has three choices: replace the concrete structures and install new generators and turbines, decommission the generating station but continue to control the flow of the river, or remove the dam entirely.

At a meeting of the legislature's Crown corporations committee last month, Liberal Roger Melanson said he has heard cost estimates of up to $3 billion to refurbish the dam.

But Thomas said it will take years before the utility will be able to decide the best option and know what the cost will be.

"Until we do the environmental impact assessment and understand the latest regulations regarding fish passage, and all the environmental requirements, you can't provide an estimate at this stage that would be reliable," he said.

The Crown-owned utility has a $4.6-billion debt but its financial plan aims to reduce that by $1 billion over the next decade.

Thomas said that by reducing the debt, it will allow NB Power to choose the best option for the dam.

David Coon, leader of the province's Green party, said the dam is a tremendous source of renewable power at a very low cost and the province would have to find an equivalent power source if it decided to decommision the dam.

"It's a huge issue," Coon said. "There are big environmental questions, big economic questions and, fundamentally, you don't want to lose the cheap renewable power."

Coon said there are many questions that will have to be addressed about the movement of salmon and other species in the river, no matter which option is picked.

He said while a decision won't be made for years, the discussion has to begin now.

Thomas said while discussion with some communities along the river has already begun, there will be greater consultation soon.

"We're thinking of putting together a community liaison group along the St. John River, and within a year or two we will begin the public consultation to get the information and explain the various options," Thomas said.