( CNN ) -- Rust-colored oil washed ashore on barrier islands off Alabama and Mississippi on Tuesday , while more patches of crude offshore appeared to be moving toward those states ' coasts , authorities reported . Researchers scrambled to clean up tar balls and puddles of oil from the beaches of Alabama 's Dauphin Island , while a strip of oil about two miles long and three feet wide stretched along Petit Bois Island , about five miles away off Mississippi , Gov . Haley Barbour 's office reported . It marked the first time oil has hit Mississippi 's shores since the largest oil spill in U.S. history erupted in late April . And while tar balls associated with the Gulf spill had hit Dauphin Island , about 35 miles south of Mobile , in early May , residents said that Tuesday was the first time they had seen oil hitting the beach . Only part of the island 's beaches have been lined with protective booms , with much of those barriers lined up near a protected wildlife area on the west end of the island . Annette Engel , a Louisiana State University researcher on Dauphin Island , said the oil is believed to be from BP 's ruptured well off Louisiana . She predicted much more would be hitting the coast in coming days -- but vacationers remained on the beach , and some were still swimming in the blue-green waters as the cleanup continued . And researchers from the Dauphin Island Sea Lab spotted large patches of the reddish-brown `` weathered '' oil during a water-sampling expedition offshore Tuesday , said John Dindo , the laboratory 's associate director . Dindo said the oil spots on the water ranged from the size of a half-dollar coin to 30 to 40 feet . A half-dozen boats could be seen skimming oil off the surface about 13 miles south of the island , he said . However , `` They were covering a very , very small spot in the ocean compared to what we saw , '' he said . The National Oceanographic and Atmospheric Administration had warned earlier this week that the spreading slick from an undersea BP oil well was heading toward the Alabama and Mississippi coasts . Dindo said tides in the area are running east and winds have been out of the southwest , driving the oil toward beach towns on the eastern side of Mobile Bay . Coast Guard Adm. Thad Allen said earlier Tuesday that authorities were investigating reports that the outer sheen of oil was reaching coastal waters off Mississippi and Alabama , but said those reports had not been confirmed . `` We 've dispatched survey teams to see what the impact is out there , and to the extent that is required , we 'll move resources that direction , '' Allen , the federal government 's national incident commander , told reporters in New Orleans , Louisiana . CNN 's Patrick Oppmann and Matt Smith contributed to this report .
NEW : Large patches of oil offshore . NEW : Nearby Mississippi island also hit . Protective booms cover only part of the Alabama island . Feds checking out spill , Coast Guard Adm. Thad Allen says .