VENICE, La.  Oil giant BP conceded Thursday that the Gulf of Mexico oil leak is larger than it originally estimated, adding more worry as portions of the massive spill began trickling ashore for the first time.

Mark Proegler, a BP spokesman, said workers are capturing about 210,000 gallons a day — the total daily amount the company and the Coast Guard have estimated is gushing into the sea — but some is still escaping. He would not say how much.

Proegler said the figure has always been just an estimate because there is no way to measure how much is spilling from the well.

Tentacles of the oil spill were seeping Thursday into Louisiana's lower marshes.

Some of the crude seeped into the Loop Current, a fast-moving current south of the well that could swing the oil east toward Florida's coastline, said Jane Lubchenco, head of the National Oceanic and Atmospheric Administration. But she said only a small amount of oil is entering the current and will likely break down by the time it nears Florida.

"The bulk of the oil on the surface is still far away from the Loop Current," she said.

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Crews have been struggling for nearly a month to cap the well that began gushing oil following last month's explosion and sinking of the Deepwater Horizon rig about 50 miles offshore. The downing of the rig killed 11 workers and sparked an ecological emergency in the Gulf.

Oil pushing into marshes ratchets up the urgency and marks the start of a complex cleanup effort, said Kurt Fromherz, a spokesman for Plaquemines Parish, who toured the oily marshes with parish leaders and Louisiana Gov. Bobby Jindal.

Pond-size sheets of oil, some of them coal-black, others bright orange or red, have wrapped around the roseau cane and other marsh features near the mouth of the Mississippi River, Fromherz said. Tar balls also washed ashore 25 miles to the west in Grand Isle.

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"The oil is no longer just a projection or miles from our shore," Jindal said in a statement. "The oil is here. It is on our shores and in our marsh."

Engineers on Sunday or Monday will attempt to pump mud into a massive device sitting over the well and choke off the flow of oil, BP spokesman John Curry said. "We are making progress."