PENSACOLA BEACH, Fla. -- The smell of oil hung heavy in the sea air. Children with plastic shovels scooped up clumps of goo in the waves. Beachcombers collected tarballs as if they were seashells.

The BP catastrophe arrived on the Florida Panhandle's white sands Friday as the company worked to adjust a cap over the gusher in a desperate and untested bid to arrest what is already the biggest oil spill in U.S. history. The widening scope of the slow-motion disaster deepened the anger and despair just as President Barack Obama arrived for his third visit to the stricken Gulf Coast.

The oil has reached the shores of four Gulf states -- Louisiana, Mississippi, Alabama and Florida -- turning marshlands into death zones for wildlife and staining beaches rust and crimson in an affliction that one person said brought to mind the plagues and punishments of the Bible.

"In Revelations, it says the water will turn to blood," said P.J. Hahn, director of coastal zone management for Louisiana's Plaquemines Parish. "That's what it looks like out here -- like the Gulf is bleeding. This is going to choke the life out of everything."

Six weeks after the April 20 oil rig explosion that killed 11 workers, the well has leaked somewhere between 22 million and 47 million gallons of oil, according to government estimates.

A device resembling an upside-down funnel was lowered over the blown-out well a mile beneath the sea late Thursday to try to capture most of the oil and direct it to a ship on the surface. But crude continued to escape into the Gulf through vents designed to prevent ice crystals from clogging the cap. Engineers hoped to close several vents throughout the day.

"Progress is being made, but we need to caution against over-optimism," said Coast Guard Adm. Thad Allen, the government's point man for the crisis. Early in the day, he guessed that the cap was collecting 42,000 gallons a day -- less than one-tenth of the amount leaking from the well. Since it was installed, it had collected about 76,000 gallons, BP said in a tweet Friday night.

Similarly, in a visit to Louisiana on Friday, Obama said it was "way too early to be optimistic" about the latest attempt to stanch the spill.

When he arrived in Louisiana, the president indicated he felt the frustration locally and from the rest of the country.

"This has been a disaster for this region, and people are understandably frightened and concerned about what the next few months and the next few years may hold," Obama said after a briefing with Allen and the governors of Louisiana, Florida and Alabama.

On his trip to Grand Isle, his motorcade passed a building that had been adorned with his portrait reminiscent of posters of him during his presidential campaign. Instead of "hope" or "change," the words "what now?" were on his forehead.

Once there, Obama rolled up his sleeves and sat down at a table with fishing industry workers, and they all ate shrimp and corn on the cob. One by one, they told Obama their horror stories, which he then related to reporters. "Terry's been shrimping out here for 45 years. Right now, things are completely shut out," the president said. "Floyd has oil seeping into these oyster beds."

As the operation went on at the bottom of the Gulf of Mexico, the effect of the BP spill was increasingly evident.

Swimmers at Pensacola Beach rushed out of the water after wading into the mess, while other beachgoers inspected the clumps with fascination, some taking pictures. Children were seen playing with the globs as if they were Play-Doh.

In Gulf Shores, Ala., Wendi Butler spotted clumps of tar in the surf and was repelled by the heavy odor of oil.

"It smells like a flight line. I know, my ex-husband was in the Air Force. He would come home from work every day smelling like this," said Butler, of Perdido Bay, Fla. "You don't smell the beach breeze at all."

On Grand Isle, where homes bear quirky names such as "Shore Thing" and "The Sand Bar," residents hung new signs before Obama's visit. "Tony Bologna," read one, a dig at BP CEO Tony Hayward. On another home, named "Mama-Pappy Dream," a new sign was added: "Dream is Gone." Still another said: "End this nightmare."