Jeff Hall, spokesman for the Unified Area Command, said tests could determine if the suspected oil is from the BP spill.
The Coast Guard sent two flights over the West Bay area near Venice on Saturday. Two boats also went out to check the waters.
Hall told The Associated Press that tests will be done Monday on water samples from an area where a marine investigator believes there's an algae bloom near Venice. The area of discolored water there was about 2.5 miles long and 300 yards wide, Hall said.
About 10 miles away, Hall said a crew spotted what appears "some kind of silvery, weathered oil." The crew in that area didn't have a sampling kit but investigators could go back out and take samples that could be tested to determine whether it's oil from the Deepwater Horizon spill, he said.
Six months after the spill started, the federal government maintains much of the oil is now gone from the Gulf. But independent researchers say they are discovering significant amounts of crude below the sea's surface, including on the ocean floor. They fear the oil that remains could harm species lower down the food chain.
The Times-Picayune reported in its Saturday editions that fishermen on Friday spotted what appeared to be miles-long strings of weathered oil, and a photojournalist with the newspaper captured the images in a flight over the water.
Hall said the material discovered Saturday that appears to be weathered oil is "away from where those photographs were taken."
The Deepwater Horizon rig exploded April 20, killing 11 people. About 172 million gallons of oil spilled into the Gulf before the well was initially plugged July 15. It was permanently sealed Sept. 19.
Robert Barham, secretary of the Louisiana Department of Wildlife and Fisheries, told the Times-Picayune that if oil is confirmed by his agency, the area will be closed again to fishing.
The Mississippi River delta is a primary wintering ground for hundreds of thousands of ducks and geese, some of which already have begun arriving. The West Bay area leads into several shallower interior bays that attract ducks, geese and myriad species of shore and wading birds each winter.