March 23, 2009--David Janka of the conservation group WWF shows off an oil-stained glove after reaching into a hole on Eleanor Island in Alaska's Prince William Sound on February 6, 2009.

Two decades after the worst oil spill in U.S. history, huge quantities of oil from the tanker Exxon Valdez still coat Alaska's shores with a toxic glaze, experts said in March 2009. (Full story: "Exxon Valdez 20 Years Later: Oil Still Remains.") .)

Of the 11 million gallons of crude oil that bled from the stranded Exxon Valdez on the night of March 23, 1989, more than 21,000 gallons (79,500 liters) remain, tucked into isolated coves and underneath the sand.

"The damage that [the spill] created is something beyond anyone's imagination," said Michel Boufadel, Temple University's Civil and Environmental Engineering chair, who has just completed research on why the Exxon Valdez oil has persisted.

—Christine Dell'Amore