Icelike crystals encrusting a 100-ton steel-and-concrete box meant to contain oil gushing from a broken well deep in the Gulf of Mexico forced crews Saturday to back off the long-shot plan, while more than 100 miles away, blobs of tar washed up at an Alabama beach full of swimmers.

The failure in the first attempt to use the specially constructed containment box over the leak 50 miles off the Louisiana coast, coupled with the ominous arrival of the sticky substance at Dauphin Island, Ala., crushed hopes of a short-term solution to what could yet grow into the worst oil spill in the nation’s history.

More than 3 million gallons of crude have spewed into the Gulf since a rig exploded April 20, killing 11, and officials said it would be at least Monday before a different solution is found.

Authorities in protective gear descended on the public beach on Dauphin Island, three miles off the Alabama mainland at the mouth of Mobile Bay and much farther east than oil had been reported.

Kimberly Creel, 41, was hanging out and swimming with hundreds of other beachgoers when crews arrived to investigate. She said she found quarter- to pea-size balls sporadically along the beach.

“It almost looks like bark, but when you pick it up it definitely has a liquid consistency and it’s definitely oil,” she said. “… I can only imagine what might be coming this way that might be larger.”

Even after discovering the oil and being warned not to touch it, Creel said beachgoers continued swimming.

Creel said it was sad to the see the oil come ashore.

“It almost brings tears to me eyes,” she said.

About a half dozen tar balls had been collected by Saturday afternoon at Dauphin Island, Coast Guard chief warrant officer Adam Wine said in Mobile. Authorities planned to test the substance but strongly suspected it came from the oil spill.

The containment box, a method never before attempted at such depths, had been considered the best hope of stanching the flow in the near term.