The Exxon Valdez oil spill occurred in Prince William Sound, Alaska, on March 24, 1989, when the Exxon Valdez, an oil tanker bound for Long Beach, California, hit Prince William Sound's Bligh Reef and spilled an estimated minimum 10.8 million US gallons (40.9 million litres, or 250,000 barrels) of crude oil. It is considered to be one of the most devastating human-caused environmental disasters ever to occur in history. As significant as the Valdez spill was — the largest ever in U.S. waters until the 2010 Deepwater Horizon oil spill — it ranks well down on the list of the world's largest oil spills in terms of volume released. However, Prince William Sound's remote location (accessible only by helicopter, plane and boat) made government and industry response efforts difficult and severely taxed existing plans for response. The region is a habitat for salmon, sea otters, seals and seabirds. The oil, originally extracted at the Prudhoe Bay oil field, eventually covered 1,300 miles (2,100 km) of coastline and 11,000 square miles (28,000 km2) of ocean.