WESTON, MASS. (WHDH) - A driver was rescued by state police after the tractor-trailer they were operating plunged into the Charles River in Weston on Saturday, officials said.

State police and Weston firefighters responding to a report of a tractor-trailer into the water near the ramp from I-95 to the Massachusetts Turnpike just before 12 p.m. found the driver standing on top of the truck, according to state police.

The driver, who cannot swim, was taken to Brigham and Women’s Hospital for evaluation, state police said. Weston Fire Deputy Chief Justin Woodside said the muddy river made the rescue difficult.

“The bottom of the river is really muddy, so they were trying to swim back but they got stuck,” Woodside said. “They were up to their waists in mud in the cold water rescue suits. The operator of the vehicle was then holding them down and they had to swim through the mud.”

A preliminary investigation determined the tractor-trailer, which had been carrying U.S. mail, veered off the road and went down a long embankment into the Charles River.

U.S. Postal inspectors have been notified, according to state police.

Drivers were asked to avoid the area of 128N near Route 30 and I-90 to 128N while crews investigate and work to clear the scene.

No additional information was immediately available.

This is a developing story; stay with 7NEWS on-air and online for the latest updates.

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