A large fuel spill that shut down the mouth of the Mississippi River for four days has had a limited impact on wildlife so far, but officials are worried about fragile wetlands downstream, according to The Associated Press. Almost 800 cleanup workers used containment booms, vacuum skimmers and other equipment Saturday to continue scrubbing oil-coated riverbanks along a 100-mile (160-kilometer) stretch of the busiest inland waterway in the United States. A tanker and a barge collided early Wednesday, spilling about 419,000 gallons (1.6 million liters) of fuel oil from the barge, closing the river from New Orleans to the Gulf of Mexico and temporarily idling some 200 oil supertankers, grain barges and other ships. The U.S. Fish and Wildlife Service had reports of almost 60 animals coated with oil, mostly ducks and wading birds, regional spokesman Tom MacKenzie said Saturday. Officials said they had reports of only limited impact on stretches of the winding river fronted by levees topped with rocky cover, concrete mats and other anti-erosion materials. But MacKenzie cautioned that canvassing such a vast area was a tall challenge and probably only a fraction of the affected wildlife had been spotted.