...Louisiana fishers Friday found miles-long strings of weathered oil floating toward fragile marshes on the Mississippi River delta...Boat captains working the BP clean-up effort said they have been reporting large areas of surface oil off the delta for more than a week but have seen little response from BP or the Coast Guard, which is in charge of the clean-up...Coast Guard Rear Adm. Paul Zukunft, in charge of the federal response, and his top science adviser, Steve Lehmann, said that little of the 210 million gallons of oil spilled into the Gulf remained on the surface or even on the Gulf's floor...Those claims...brought quick rebuttals from a variety of environmental and fishermen's groups...[LSU environmental sciences professor Ed Overton] "these reports are of mats of weathered oil, and that can cause serious problems if it gets into the marsh"...