As the BP oil spill inexorably evolves into the world’s worst environmental disaster, Florida State University oceanographer Ian MacDonald warns that the oil could wash up on European shores before the end of summer.

“It’s entirely possible,” MacDonald, a professor of oceanography at Florida State, said in an interview published in The Sunday Times of London on June 13. “These tar balls are incredibly persistent, and once they get into the Gulf Stream, they’ll be there until they get washed ashore.” His warning was echoed by Jean-Michel Cousteau, son of the famous underwater explorer Jacques Cousteau.

“The oil is going to get into the Gulf Stream,” he said, “to Britain, to France, to Spain.” The warnings come as signs appeared for the first time on beaches along the Florida Panhandle warning beachgoers not to swim or fish in the water.