President Barack Obama has played the role of tourism chief on his trip to USA’s Gulf Coast this week, saying the region remains “outstanding” and “open for business” despite the country’s worst environmental disaster in history.

He promised local residents and businesses that the beaches would be restored to their “pristine condition”, and left in better shape than before the BP oil spill.

On his fourth visit to the region since the crisis started, he said: “There’s still a lot of opportunity for visitors to come down here. There are a lot of beaches that have not been affected and will not be affected.”

“And we just want to make sure that people who have travel plans down to the Gulf area remain mindful of that,” added the US president. “Because if people want to know what can they do to help folks down here, one of the best ways to help is to come down here and enjoy the outstanding hospitality.”

Obama and leaders must play a careful balancing act. On the one hand they must warn about the impact of the spill and attempt to minimise its impact, but also avoid alarming tourists and hurting the local tourism industry.

His fourth tour to the region includes Pensacola, reflecting the oil slick’s arrival to the Florida Panhandle.

While some beaches on the coastline may appear to be untouched, oil from the blown-out BP well continues to spoil significant parts of the shoreline and has already penetrated into critical marshlands, threatening breeding grounds for wildlife, waterfowl and sea creatures - in particular shrimp and oysters.

Hotel bookings are down as much as 30 percent in parts of the Panhandle during its high tourism season, apparently because of the spill and fears it will ruin the fine white sand beaches.

According to the US Coast Guard, about 120 miles of the Gulf coastline has been affected, and large resorts are preparing for the worst.

Bookings to Orlando and the East Coast appear less affected. Both Virgin Holidays and Thomson said they had seen no change in booking patterns.

Meanwhile a leading oceanographer has warned that the oil could wash up on European shores before the end of summer.

“It’s entirely possible,” Dr Ian MacDonald, of Florida State University told The Times. “These tar balls are incredibly persistent, and once they get into the Gulf Stream, they’ll be there until they get washed ashore.”

Jean-Michel Cousteau, son of the famous underwater explorer Jacques Cousteau, also voiced the same concerns.

“The oil is going to get into the Gulf Stream,” he said, “to Britain, to France, to Spain.”