It's hard to believe this occurred 20 years ago, but on March 24, 1989, the oil tanker Exxon Valdez spewed 10.8 million U.S. gallons (approximately 40 million litres) of crude oil into Prince William Sound, Alaska. The oil dispersed over 11,000 square miles (28,000 square kilometres) of ocean.

Somewhere between a quarter of a million to half a million seabirds perished, along with 1,000 sea otters, 300 harbour seals, 250 bald eagles, and 22 killer whales. Billions of  salmon and herring eggs were also destroyed.

The effects of the spill were still being felt years after the initial cleanup according to researchers from the University of North Carolina. They found oil had persisted in large quantities for years after the spill in subsurface reservoirs. Many species suffered long-term loss, including high mortality among incubating pink salmon eggs for at least four years after the spill; even when oil chemicals in the waters were only a few parts per billion.

Marine mammals and sea ducks continued to be killed years after the accident partly due to their eating of creatures contaminated by the hidden oil and direct contact with the oil. Species such as sea otters, harlequin ducks and killer whales also suffered sizeable, long-term losses. Affected mussel beds and other tidal shoreline habitats will take an estimated three decades years to recover, according to the researchers.

Here in Australia we had a sizable oil spill recently that marred some extraordinary coastline in Queensland. When it was first reported, we were led to believe it was *relatively* minor, but as the days rolled on the initial 20 to 30 tonnes reported by the ships owner as having been lost grew to 230 tonnes, covering 60 kilometres of beaches. Additionally, around 30 shipping containers of ammonium nitrate were also lost.

These days, the argument about oil in terms of the environment is usually around greenhouse gases; but we should't forget that at any point in time, there's many millions of tonnes of the stuff being floated around the world and when spilled, a little bit goes such a long way.

Learn more about the effects of oil spills