U.S. President Barack Obama began his third visit to the Gulf Coast by saying that, while he believes some progress has been made against 45-day-old oil spill, it's still "way too early to be optimistic."

He also criticized BP for launching an ad campaign and paying out dividends to its shareholders during the crisis. At the same time, he said he did not want to see the company "nickeling and diming fishermen or small businesses here in the Gulf who are having a hard time."

"I want BP to be very clear," he said. "They have moral and legal obligations here in the Gulf for the damage that has been done," he said.

Obama made his comments at the airport in New Orleans before departing to gauge the response to the disaster, as frustration mounts at the growing slick of crude in the Gulf.

From New Orleans, Obama bounded on a two-hour motorcade drive to Grand Isle, a small barrier island, to hear from the people.

Along the way, he passed this roadside sign: "HELP US NOW!!"

Obama went to a bait shop to talk to fishing industry workers about how the disastrous oil spill is affecting their business.

The mayor of Grand Isle, David Camardelle, choked up as he told the president of staying up nights worrying, "looking at the ceiling fan."

"We don't know what's going to happen tomorrow," Camardelle said.

Obama later talked with other Grand Isle residents, promising them: "We're not going to forget that this is a way of life."

"Even when I'm not here, I'm thinking about you," he said.

Crude reaches Florida

Meanwhile, tar balls began washing up on Florida's Pensacola Beach earlier on Friday, even as BP engineers tried to place a sophisticated cap over the blown-out well that has leaked millions of litres of crude oil into the Gulf of Mexico.

CTV's Joy Malbon said the rust-coloured tar balls, ranging from coin- to basketball-sized, are scattered across the popular tourist destination.

After a short walk on the beach, her shoes were covered in oil, Malbon told CTV.ca in a telephone interview.

"They are all over the place, some are bigger than others," she said.

The official Pensacola Beach website reported that an "oil sheen" was seen about 16 kilometres from shore on Thursday.

But swimmers at Pensacola Beach rushed out of the water after wading into the mess while others inspected the clumps with fascination, some taking pictures.

The spill has struck four states on the Gulf coast, but Louisiana has been hit hardest. Brown pelicans coated in oil that resembled chocolate syrup flailed and struggled in the surf on a Louisiana island, and beache have been stained in hues of rust and crimson like the colour of drying blood.

Far out to sea and 1,500 metres underwater, BP engineers were using remotely controlled submersibles to adjust the inverted funnel-shaped cap placed over the leak.

Oil continues to leak

The device was set over the leak late Thursday, but crude continued to spew into the sea adding to what is already the worst oil spill in U.S. history. Engineers hoped to close several open vents on the cap throughout the day in the latest attempt to contain the oil.

The cap has been designed with an interior seal to hold back the spewing oil, but engineers say it is not perfect and there will be some seepage.

Malbon said that BP believes it will know more about the lid's effectiveness within the next 12 to 24 hours. Underwater video footage appears to show oil still coming out of the well.

"The problem is they sliced off that leaking pipe with shears, so the cut was not as precise as they had hoped and what they were hoping for is when they put that seal on that it would be a better fit," Malbon said from Pensacola Beach.

"So, we're not quite sure how much of that oil is being suctioned off, hopefully we'll get some news on that today."

Authorities guarded

With so many failed attempts to cap the leaky well in recent weeks, authorities are guarded in their evaluations of any progress the current effort is making.

"Progress is being made, but we need to caution against over-optimism," said U.S. Coast Guard Admiral Thad Allen, the government's point man for the disaster.

Allen said that "even if successful, this is only a temporary and partial fix and we must continue our aggressive response operations at the source, on the surface and along the Gulf's precious coast line."

The device has different colored hoses loosely attached to combat near-freezing temperatures and icylike crystals that could clog it. It started pumping oil and gas to a tanker on the surface overnight, but it wasn't clear how much.

Robots a mile beneath the Gulf were shooting chemical dispersants at the escaping oil -- though it looked more like flares when illuminated a mile underwater.

He said a very rough estimate of how much of the leaking oil is being collected would be about 158,000 litres a day, though he stressed that information was preliminary.

"Once the containment cap is on and it's working, we hope the (leak) rate is significantly reduced," he said.

Since the deadly explosion on the Deepwater Horizon rig started the leak, an estimated 21 million to 46 million gallons of oil have seeped into the ocean.

With files from The Associated Press