Coastal real estate in America is so often depicted in images of sprawling mansions with long lawns leading down to boat slips and sandy beaches. They grace the cover of vacation magazines and retirement brochures. But the reality is that the majority of coastal homes are not super swanky, and they are most in danger of rising sea levels.

If sea levels were to rise 6 feet, 1.9 million homes, or $916 billion worth of U.S. residential real estate, could be lost, according to a new report from Zillow. Zillow looked at what types of homes would be flooded, absent preventative measures, based on the most recent estimates of sea-level increase by the end of the century.

“Living near the water is incredibly appealing for people around the country, but it also comes with additional considerations for buyers and homeowners,” Zillow chief economist Svenja Gudell wrote in the report. “Homes in low-lying areas are also more susceptible to storm flooding and these risks could be realized on a much shorter timeline as we have seen time and time again.”

Zillow found that 39 percent of homes expected to be underwater by the year 2100 are in the most valuable category. The rest are around the median price, about $220,000, or below. One-quarter are among the least valuable homes. Exacerbating the issue is that owners of lower-priced homes likely don’t have the resources to take preventative measures against the rising tides, like putting in sea walls or making changes to foundations to withstand intermittent flooding.

“We’ve seen the enormous impact flooding can have on a city and its residents,” said Gudell. “It’s harder for us to think about it on a long-term timeline, but the real risks that come with rising sea levels should not be ignored until it’s too late to address them.”

The parade of hurricanes this year either damaged or destroyed thousands of homes in Houston, Florida and Georgia. What came as a shock to so many was that it wasn’t all coastal damage. Hurricane Harvey managed to submerge homes that were a long drive from the Texas coast. Rivers and reservoirs were the culprit, after storm surges from the rising ocean and relentless rain filled them beyond capacity.

The majority of homes at risk of flooding, 65 percent according to Zillow, are in suburban areas, like those flooded in Houston. Just under 23 percent are in urban locations, and just 12 percent are in rural areas.

Of the nation’s largest cities, Miami, New York, Boston, Tampa and Fort Myers, Florida, have the highest volume of homes at risk of flooding. Los Angeles, Charleston, South Carolina, Houston and New Orleans are also in the top 20 markets at risk.