An American ecologist says experience in the northwest United States shows a river's ecosystem can return to its natural form after the removal of a dam.

Jeff Duda is a research ecologist at the U.S. Geological Survey and looked at the the recent removal of two dams from the Elwha River in Washington.

"We're still seeing downstream, kind of responses," said Duda. 

"The river reset. But the river's been very efficient at moving sediment through the river.

"Generally though, we see that rivers are pretty resilient. They can adjust and deal with these sediment issues and respond in a way that we have some idea it's going to be OK on the other side."

Removal of the Mactaquac dam is one of three options being considered by NB Power as the Crown utility confronts the premature end of life of the hydroelectric generating station by 2030.

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NB Power needs to rebuild or remove the Mactaquac dam before the end of its life in 2030. (CBC)

Replacing the dam and powerhouse to generate electricity is also an option. Also being explored is the option of replacing the dam, but without power generation so the headpond behind the dam would be retained.

Depending on which option is chosen, the cost of the Mactaquac project could run as high as $5 billion, according to NB Power. That would make it the largest infrastructure project ever undertaking by the utility.

Lecture at UNB

With the options for Mactaquac still being explored, Duda was in Fredericton to deliver the annual Dineen Lecture at the University of New Brunswick on Tuesday.

"They'll hear a story of a fascinating, majestic river on the northwest of the United States," said Duda.

"It's a story, kind of a rebirth of a river."

Duda said the Glines Canyon dam may be the largest dam ever removed in the world.

However, if the Mactaquac dam were to be removed, it would dwarf the Elwha dam removals.

The largest of the two dams removed was the Glines Canyon dam. It was 64 metres high, which is nine metres higher than the Mactaquac dam.

However, the Glines Canyon Dam was much narrower than the earthen Mactaquac dam, which is 518 metres in length.

The two dams on the Elwha River had reservoirs covering about 170 hectares behind the Glines Canyon Dam and about 110 hectares behind the Elwha Dam.

The reservoir, or headpond, behind the Mactaquac dam covers more than 8,100 hectares.