The US dumped vast quantities of nuclear material off its coasts between 1946 and 1970—more than 110,000 containers, says one official count. Today, the whereabouts of many of those 55-gallon drums and other containers is a big question mark, the Wall Street Journal reports. "Many were not dropped on target," according to a 2010 federal report. Their location is just one of several major questions raised by the Journal. It's also unclear, for instance, how many dump sites there were: Government reports have given numbers ranging from 29 to 60. Then there's the question of how much radioactivity persists, since some isotopes can stay radioactive for thousands of years.
Potential fish contamination poses another concern. A 1991 report on a site off San Francisco suggested some contamination, but there was no follow-up study—despite a California law calling for annual assessments. The state now says the site should be handled by the federal government, which in a 2001 study found only "very low levels" of radioactivity in local sediment. The barrels are spread across some 540 square miles of ocean floor, the National Oceanic and Atmospheric Administration said in 2010, and only 15% of it has been assessed. The agency says it wants to investigate the site further, but it doesn't have the money. Click for the Journal's full report. (Read more nuclear waste stories.)