Twenty years after the Exxon Valdez spilled 11 million gallons of crude oil in Alaska's Prince William Sound, oil persists in the region and, in some places, "is nearly as toxic as it was the first few weeks after the spill," according to the council overseeing restoration efforts. "This Exxon Valdez oil is decreasing at a rate of 0-4 percent per year," the Exxon Valdez Oil Spill Trustee Council stated in a report marking Tuesday's 20th anniversary of the worst oil spill in U.S. waters. "At this rate, the remaining oil will take decades and possibly centuries to disappear entirely."

The council's findings come two decades after the March 24, 1989 disaster, when the single-hulled Exxon tanker hit a reef, emptying its contents into Alaskan waters. The spill contaminated more than 1,200 miles of shoreline and killed hundreds of thousands of seabirds and marine animals. The council, made up of three state and three federal appointees, was created to administer the $900 million that Exxon paid to settle lawsuits filed after the accident, which also resulted in criminal charges against the ship's captain, Joseph Hazelwood. Hazelwood, was accused but then acquitted on a charge of being drunk at the time. He was, however, convicted of negligent discharge of oil, a misdemeanor, and sentenced to a $50,000 fine and 1,000 hours of community service.

Learn more about the 1989 Exxon Valdez oil spill and lawsuits prosecuted on behalf of local fishermen.