Lake Pontchartrain, which has until now been free of oil from the BP spill, is now home to tar balls and an oil sheen.
For the first time since the accident, oil from the ruptured well is seeping into Lake Pontchartrain, threatening another environmental disaster for the huge body of water that was rescued from pollution in 1990s to become, once more, a bountiful fishing ground and a popular spot for boating and swimming.
Over the July Fourth weekend, tar balls and an oil sheen pushed by strong winds from faraway Hurricane Alex slipped past lines of barges that were supposed to block the passes connecting the Gulf of Mexico to the lake.
State authorities closed the lake's eastern reaches to fishing on Monday, though most of it remained open. Barges were lined up at bayous and passes to stop the oil from coming in, and cleanup crews Tuesday used nets to collect tar balls from marinas and docks. They also planned to lay out 9,000 feet (2,700 meters)of special permeable booms. But the lake was too choppy for skimmer vessels to operate.