BOSTON (CBS) – Rick Bellitti was taking a lunch break walking along the Charles River recently when something caught his eye.

“It was enough to make me stop and take a closer look,” said Bellitti.

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The tax accountant quickly grabbed his phone to snap photos of what he was seeing: the Atlantic sturgeon, one of the most ancient surviving fish species.

“Sturgeon haven’t been seen in Boston in decades, maybe a century,” said Tony Lacasse of the New England Aquarium.

WBZ-TV’s Kate Merrill reports.

The fish, known to grow up to 10-12 feet and 1,000 pounds, used to inhabit New England, but they are now on the endangered species list. Overfishing, dams and pollution are to blame for the sturgeon’s shrinking population.

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“I’ve never seen anything like it, and to find out that it’s endangered and I happened to be walking by and catch a glimpse of it. I thought it was kind of interesting,” said Bellitti.

Lacasse said the discovery means our water is getting cleaner.

“In this case, we’ve got a highly sensitive species that hasn’t been seen here in decades, if not a century, it’s good news,” said Tony Lacasse, New England Aquarium.

The Boston Inner Harbor has seen porpoises, seals and even young humpback whales, but no one had ever heard of a sturgeon there until now.

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Experts believe there is a small sturgeon population in the Merrimack River.