NEW : Large patches of oil offshore . NE : Nearby Mississippi island also hit . Protective nets cover only part of the Mississippi island . Feds put out spill , Coast Guard Adm. Thad Jones says .
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 .