By Erwin Seba ROBERT, La., May 10 (Reuters) - The huge slick from the Gulf of Mexico oil spill threatened Louisiana shores west of the Mississippi Delta on Monday as BP Plc said it was trying several options to control the leak without being sure they would work. National Guard helicopters in Louisiana's Lafourche Parish were preparing to drop sandbags onto outlying island beaches to try to block oil from getting into fragile marshlands teeming with wildlife and seafood fisheries. "It's easier to clean oil from a beach than from a marsh," parish spokesman Brennan Matherne told Reuters, saying the aim was to try to use a 15-mile (25 km) barrier beachline as a natural protection for the more vulnerable wetlands inshore. Fears were growing of a prolonged environmental and economic disaster for the U.S. Gulf Coast after a weekend setback in an initial undersea maneuver by BP to contain the spill, which could become the worst in U.S. history. BP said on Monday it had incurred $350 million in costs from the spill, suggesting the final bill could be much higher than many analysts predicted. BP shares were down 0.8 percent at 12:30 p.m. (1430 GMT), lagging a 4.1 percent rise in the STOXX Europe 600 Oil and Gas index. The stock dropped as low as 540.7p, its lowest since November. BP stock has lost about 15 percent since the Deepwater Horizon rig caught fire on April 20, killing 11 people, wiping around $30 billion from BP's market value. The projected westward spread of the massive slick, swelled by crude gushing unchecked from a ruptured BP-owned seabed well, has raised fears of an impact on rich fisheries areas filled with shrimps, oysters, crabs and crayfish, and even on major shipping channels off the Louisiana coast. One investment firm, Bernstein, has estimated a potential $2.5 billion cost to Louisiana's fishing industry from the spill, which is already affecting Gulf Coast tourism. The Louisiana Offshore Oil Port (LOOP), the nation's only deepwater oil terminal located southwest of New Orleans, said vessel movements were unaffected. "LOOP has seen some sheen from the oil spill at its marine terminal but it has not impacted our operations," spokeswoman Barb Hestermann said in an email. SOLUTIONS UNCERTAIN BP Chief Operating Officer Doug Suttles said the company, facing enormous pressure from the U.S. government and public, was pursuing several possible technical solutions in a bid to contain its gushing seabed well and eventually plug it. "What we've been doing is pushing parallel paths because we don't know which one's going to work," he told CNN. After a buildup of crystallized gas stymied an initial attempt by BP to place a large containment dome over the well leak, Suttles said the company was now considering trying to fit a smaller "top hat" dome over the fissure. The aim would be to then funnel the captured oil to a surface tanker. Other options included trying to block the well's failed blowout preventer with a "junk shot" of rubber or other materials, or fitting a new valve or preventer. A relief well being drilled to try to finally plug the ruptured well could still take 75 to 80 days to complete. "We've brought the world's experts together to try to help us understand how do we make these successful," Suttles said on NBC's "Today" show. "I can't tell you if any one of them will work but as long as we have options we're going to keep trying. The goal here has to be to get the flow stopped." Pressed about reports that the unchecked oil flow, estimated initially at to be at least 5,000 barrels (210,000 gallons/795,000 litres) per day, could end up gushing as high as 60,000 barrels a day, Suttles told NBC: "It's possible but it's very, very unlikely for that to happen." RISK OF MORE OIL ONSHORE The environmental group Greenpeace issued an unconfirmed report late on Sunday that said traces of oil had been found onshore at Port Eads, the southernmost point of Louisiana. But a spokesman for Louisiana's Plaquemines Parish said there were no reports of oil on land. The spill's major contact with the shoreline has been in the unpopulated Chandeleur Islands off Louisiana, which is a mostly a wildlife reserve and bird sanctuary. A 24-hour forecast from the National Oceanic and Atmospheric Administration said winds could push oil ashore in the Mississippi Delta, Breton Sound, the Chandeleur Islands and areas directly north. BP said in a statement its costs included spill response, containment, relief well drilling and payments to Gulf Coast states to speed their response plans. The final bill could be much higher than many analysts predicted as leaking oil continues to spew uncontrolled into the Gulf. The spill threatens economic and ecological disaster on Gulf Coast tourist beaches, wildlife refuges and fishing grounds across four states. It has forced President Barack Obama to rethink plans to open more waters to drilling. The two Louisiana parishes directly west of the Mississippi Delta declared states of emergency on Sunday. Tar balls washed up on Alabama's Dauphin Island, a barrier island and popular beach resort, during the weekend and local tourism operators said vacation traffic had already slowed to a trickle because fears of the spill's impact. FRUSTRATION, SADNESS "It makes me so sad. You take so many things for granted: a beautiful beach, fresh shrimp whenever you want it. It is so frustrating there seems to be no answers for it," said Dauphin Island resident Joyce Carroll, a former air stewardess. Fishing is suspended in parts of the Gulf waters and much of the Louisiana coast. Many tourists have been scared away by reports of reddish, putrid water offshore, even though the coast is currently unaffected. Top officials from BP and some of the other companies associated with the ruined Deepwater Horizon drilling platform are expected to get a grilling at congressional hearings on Tuesday and Wednesday. The U.S. Coast Guard and the U.S. Minerals Management Service also plan an investigation into the drilling rig's sinking, starting in Kenner, Louisiana, on Tuesday. Delays in containing the leaking well increase the chances it could become the worst U.S. oil spill, surpassing the 1989 Exxon Valdez disaster in Prince William Sound, Alaska. (Additional reporting by Anna Driver in Houston; Pascal Fletcher in Miami; Steve Gorman and Verna Gates on Dauphin Island, Alabama; Tom Bergin in London; Haitham Haddadin in New York; Writing by Pascal Fletcher; Editing by Bill Trott) Keywords: OIL RIG/LEAK . 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