Smoothly and with barely a sound the, until now, largely static Twin Sails Bridge proved it had plenty of life in it.

The triangular sails glided across a blue sky to open and close in around two minutes, signalling a significant stage as it nears the end of its 20-month construction.

“I think it’s magic,” said a delighted Borough of Poole council leader, Cllr Elaine Atkinson, watching the £21m structure in operation for the first time.

“The leaves are soaring into the autumn sun.”

She has overseen the bridge throughout its construction and build period, visiting Cleveland Bridge where the metal was fabricated, seeing it arrive on site and slowly stretch across the Back Water Channel from Hamworthy to the old town.

“It’s inspirational,” she said. “It’s a world class bridge for a world class town.”

The bridge’s two triangular-shaped leaves are lifted by two hydraulic rams on each, and are expected to operate 11 to 13 times a day, in conjunction with Poole Bridge.

The 140m-long bridge has a 19m wide navigation channel and the lift spans pivot through 88 degrees as they open.

The two bridges are computer operated from a control room on site with unrestricted views and the consecutive opening should mean one is always available for road traffic.

Ten cameras on Poole Bridge and more on the new bridge will give all-round views.

“It will work,” said Paul Spencer, the borough’s operations centre manager.

Steve Thompson, who led the design team for Gifford (now part of Ramboll), said of the bridge: “I think it’s fabulous. It’s a challenging project for everyone but it’s gone very smoothly.”

It may be going up and down but the work is far from finished, with walkways, light-totems, the carbon-fibre masts and much more to do before completion in January.

Richard Bruten, project manager for Hochtief (UK) Construction Ltd, said there would be some channel closures as they laid the road surface.

“We will try not to cause too much disturbance to the marine traffic,” he said.

• The Twin Sails Bridge could have its own music to celebrate its opening next year.

The BSO’s children’s composer is working with Poole schools to compose a piece for the bridge.