Thousands of protesters are gathering in Lafayette Square across from the White House exactly one year out from the presidential election to oppose a plan for a transnational oil pipeline they fear could harm the environment.

More than 8,000 people linked hands around the White House to oppose the Keystone XL project, a pipeline that would carry oil derived from tar sands in Alberta, Canada, to refineries in Houston and Port Arthur, Texas.

Bill McKibben, one of the protest organizers, described the scene as either "a big O-shaped hug" or "a symbolic house arrest."

Obama missed most of the protest while he played golf at Fort Belvoir in Virginia on Sunday afternoon.