NEW ORLEANS  A sheen of oil coated the Mississippi River for nearly 100 miles from the center of this city to the Gulf of Mexico on Friday following the worst oil spill here in nearly a decade. Around noon, after two days with no ship traffic, the Coast Guard opened the river to limited use.

The thick industrial fuel pouring from the barge could be smelled for miles in city neighborhoods up and down the river, even as hundreds of cleanup workers struggled to contain the hundreds of thousands of gallons. Some environmentalists worried about reports of fish and bird kills in sensitive marsh areas downstream, though officials said they had so far heard of only a handful of oil-covered birds. Booms to protect areas richest in wildlife, at the river’s mouth, were being deployed, officials said.

The Mississippi had been closed to all boat traffic, stranding about 200 vessels. The Coast Guard said 58 vessels were stopped in the river, the Associated Press reported Friday morning, and 97 were waiting at Southwest Pass — the narrow entrance from the Gulf of Mexico into the river. Another 37 were waiting on the Intercoastal Waterway, a shallow canal system that extends across the Gulf Coast. Forty-eight more were en route and expected to arrive over the weekend, and it could take days to clear the backlog.

The effect on the area’s economy was thought to be significant, with this city’s port estimating a loss of at least $100,000 a day and probably more while the river was closed, and petrochemical facilities dependent on it for shipping were threatened with a bottleneck, the Coast Guard said. Some suburbs stopped drawing drinking water from the river.