As an institution devoted to telling the story of the sea, the Mystic Seaport Museum has an inherently close relationship with water. Sitting along the Mystic River in southeastern Connecticut, its campus spans 19 acres and nearly 150 structures, including exhibition spaces and a re-creation of a 19th-century New England coastal town. Along the museum’s waterfront, it has an active seaport and a marina where roughly 900 boats dock annually.

For nearly a century, the organization has maintained a harmonious relationship with the river. Flooding caused by storms, high tides and heavy winds occurred occasionally, but were not cause for great alarm.

However, with storms becoming more severe and sea levels expected to rise substantially in the coming decades, the museum faces a daunting challenge: how to stave off the inevitable. Planning has begun to protect the museum’s history and properties, but the scope of the effort, as well as the costs, are immense.

Nevertheless, the museum may have little choice.

“Twenty years ago, there might have been an inundation a few times a year,” Chad Frost, principal of the landscape architecture firm Kent and Frost, which has been working with the museum for two decades, said in a video interview. “Now, we’re seeing degrees of flooding on a monthly, sometimes weekly, occurrence.”

The museum’s location has made it especially vulnerable. It was constructed on the site of an 1830s shipyard built by three mariner brothers, George, Clark, and Thomas Greenman. They, like other entrepreneurs in the booming seafaring community of Mystic, took over low-lying and marshy lands whose gently sloping banks and proximity to the Atlantic Ocean were opportune for shipbuilding. When the museum was established in 1929 as the Marine Historical Association, a steady expansion began, with land filled in and bulkheads added along the river.

“This kind of development was happening along the entire Connecticut coast around 100 to 80 years ago,” Frost said. “Now we know that fill settles over time. Add to that the fact that we didn’t have the foresight to know about climate change and rising sea levels — areas once habitable are being forced to adapt.” Today, the majority of the campus is in a FEMA-designated flood zone. Among the highest points — at just 14 feet above sea level — are the museum’s offices, which were originally the Greenman brothers’ homes.

“It’s a testament to how forward-thinking these mariners were,” said Shannon McKenzie, the museum’s vice president of watercraft operations and preservation, in a video interview. “They knew the river would be a threat long before people were concerned about sea level rise.”

Flooding often submerges walkways throughout the campus, preventing visitors from accessing buildings and experiences. Some structures, especially those along the waterfront like the Thomas Oyster House — which operated in the thriving oyster distribution hub of New Haven from 1874 to 1956 and was donated in 1970 and placed on its current site on a museum pier in 1984 — also become flooded.