VENICE, La. — The surface area of a catastrophic Gulf of Mexico oil spill quickly tripled in size amid growing fears among experts that the slick could become vastly more devastating than it seemed just two days ago. Frustrated fishermen eager to help contain the spill from a ruptured underwater well had to keep their boats idle Saturday as another day of rough seas kept crews away from the slick, and President Barack Obama planned a Sunday trip to the Gulf Coast. Documents also emerged showing British Petroleum downplayed the possibility of a catastrophic accident at the offshore rig that exploded. How far the spill will reach is unknown, but the sheen already has reached into precious shoreline habitat and remains unstopped, raising fears that the ruptured well could be pouring more oil into the Gulf than estimated. The Coast Guard estimates now that at least 1.6 million gallons of oil have spilled since the April 20 explosion that killed 11 workers.