A new government report details 87 shipwrecks — most sunk during World War II decades ago — that could pollute U.S. waters with tens of millions of gallons of oil.

Even so, the potential for pollution is less than scientists had expected. The report released Monday by the National Oceanic and Atmospheric Administration concludes “the scope of the problem is much more manageable than initially feared. … Our coastlines are not littered with ‘ticking time bombs.’”

Agency officials estimate that far less oil will leak into the ocean than the BP oil spill of 2010, which spewed roughly 200 million gallons into the Gulf of Mexico alone.

“That’s not a bad number in comparison to what we first thought it would be,” said NOAA’s Lisa Symons, who wrote the study.

There are 20,000 shipwrecked vessels that lie off the nation’s coastlines. Most of those either finished leaking long ago, ran on coal instead of oil, are too small or aren’t near vulnerable land.

“There are only six that really keep me up at night, but we don’t know where they all really are,” Symons said. Those six have the biggest potential to foul coastal areas because even if they spill only 10 percent of their oil, they could cause a local-scale disaster, she said. They don’t have to be a worst-case spill to be a disaster.

Of those six, Symons said NOAA doesn’t know the exact location of three of them, just where they were last seen before they sank. Three of the six worst potential problems are off Florida, one near Georgia, one near South Carolina and one near New York. Some are as close as 15 miles from shore.

Of the overall 87 ships identified as potential polluters, 52 were lost in World War II, mostly up and down the Atlantic coastline.

Others were lost in crashes, fires and storms, including the Edmund Fitzgerald. The story of that ship’s sinking in Lake Superior was turned into a classic 1970s ballad. Two ships, including the Edmund Fitzgerald, aren’t even in U.S. waters but are close enough they can pollute American waters, NOAA officials said.

The agency has identified 17 ships that have a known location and that need to be investigated further to see if the oil could be removed. Removing oil in advance, before it leaks, is far easier than waiting till after it spills into the water, Symons said.