(FORTUNE Magazine) – Next spring, when winter storms subside in Prince William Sound, teams of scientists from the National Oceanic and Atmospheric Administration, the state of Alaska, the Coast Guard, and Exxon will hit the beaches. They will be searching for what remains of the oil spilled by the tanker Exxon Valdez in March 1989 -- and they won't find much. Thanks to pounding surf, some remarkable microbes, and a lot of human toil, most of the beaches that were soiled by the spill are clean. Not that all of the oil is gone. Some that seeped into crevices between rocks in certain places remains hidden below the surface. John Robinson, chief of NOAA's hazardous materials response branch, estimates that at the end of last summer between 250,000 and 1.2 million gallons (between 2% and 11% of the oil spilled) were still imbedded under the beaches, with the lower estimate being the likelier. But, says Robinson, ''we tend to believe the remaining oil doesn't pose as much risk as some of the measures it would take to get it out.'' The oil is most likely to remain in those places where it does the least harm. It tends to penetrate porous beaches with large rocks and big crevices that are not rich biological habitats, and in any case most of the toxic elements of the oil have long since evaporated. To remove what's left, heavy earthmoving equipment would have to turn over the beaches, exposing oil as deep as a yard to the cleansing of the waves. Exxon is testing this technique on several beaches this winter. But experience in previous spills, notably the wreck of the huge Amoco Cadiz off the coast of France in 1978, indicates that ripping up beaches only adds to the destruction of habitat and delays nature's recovery. That lesson is worth remembering at perhaps the most soiled site in Prince William Sound, a two-acre salt marsh on Knight Island known to helicopter pilots who have been working on the cleanup as the Bay of Death. Here the oil has penetrated into a thick layer of mud that gets little or no cleansing from wave action. If the soiled muck is carted away as it was from some marshes after the Amoco Cadiz, it could be many years before plants and animals reestablish themselves in the marsh. Robert Clark, who recently retired as head of marine biology at Britain's University of Newcastle and is founding editor of Marine Pollution Bulletin, found grasses and barnacles flourishing in the salt marsh last summer. Says he: ''Experience says it will recover a damn sight faster on its own. Let nature take its course.''

The best technique for cleaning the remaining oil may be the nifty partnership between man and microbe called bioremediation. Certain bacteria in the earth's seas and soils eat hydrocarbons. They probably live mostly on oils given off by living or newly dead plants and animals, but they are not picky eaters. Cleanup crews in Prince William Sound have been powdering the beaches with nitrogen and phosphorous similar to common garden fertilizer. This causes the bacteria to multiply rapidly, and they then gobble the crude oil. Under development: a pelletized version that would penetrate into the lower crevices of Prince William Sound's beaches. Arco has successfully tested the technique on bacteria found in the Arctic (Prince William Sound is far below the Arctic Circle, at about the latitude of Leningrad), which means it could someday help keep Prudhoe Bay and ANWR clean of oil mishaps. The waters of Prince William Sound appear even cleaner than the beaches. Robinson of NOAA says, ''Evidence of slight exposure to oil has been found in some fish, but there is no evidence of danger, even for those who live on fish alone.'' The fish appear to have multiplied. Herring fisherman reported record catches last summer, and the harvest of pink salmon set a record, 44 million fish, 40% more than in the previous summer. The salmon catch was made up of fish that swam out to sea through Prince William Sound just after the Exxon Valdez went aground. In addition to advances in cleaning up oil, the industry is taking a lot more precautions against spills. Previously, tankers were escorted by a pilot boat through a narrows about two hours from Valdez and then left on their own. Today tankers are escorted to open ocean, a journey of eight hours, by two oceangoing vessels, each capable of towing a fully loaded tanker. When ice drifts into the shipping lanes, tankers are required to slow to four knots (five miles per hour). A collision with ice at that speed only scratches the paint, says Michael Williams, vice president for the environment at Alyeska, the consortium of companies that operates the trans-Alaskan pipeline and the loading terminal at Valdez. Before the oil spill, tankers would leave the shipping lanes to avoid ice in their path, a maneuver the Exxon Valdez was carrying out when it ran into trouble. Alyeska now has enough equipment, including 30 miles of booms and five barges, to skim 25,000 barrels of oil per hour off the ocean. At that rate -- assuming calm seas and favorable winds -- the entire Valdez spill might have been mopped up in ten hours. As it is, Exxon has spent 20 months and $2.2 billion on the Valdez mess. And a company spokesman vows: ''We are ready to go back in next summer and do whatever is necessary.''