BP backed down Thursday from its plans to dump more pollution into Lake Michigan, but critics want the oil giant to ensure its promises are legally binding.

Responding to a month of unrelenting criticism from politicians and the public, BP pledged it will not invoke provisions of a new permit that allows the largest oil refinery in the Midwest to release significantly more ammonia and suspended solids into the lake.

BP, which promotes itself as environmentally friendly, said it would abide by more stringent limits in its previous permit as the company moves forward with a $3.8 billion expansion of its Whiting, Ind., refinery, the nation's fourth largest.