BATTLE CREEK, Mich.  Gov. Jennifer M. Granholm expressed growing worry on Wednesday that an oil spill, believed to be among the largest ever in the Midwest, might reach Lake Michigan if efforts to contain the oil were not strengthened.

“It would be a tragedy of historic proportions if this reached Lake Michigan,” Ms. Granholm said.

More than 800,000 gallons of oil spilled Monday into the Kalamazoo River, a major waterway that flows into Lake Michigan, about 60 miles away. The leak came from a 30-inch pipeline that carries millions of gallons of oil each day from Griffith, Ind., to Sarnia, Ontario.

Response crews worked Wednesday to contain the oil spill, which had already reached at least 35 miles of the river and left fish and birds coated in oil.

On the river on Wednesday, Dan Backus arrived at his favorite fishing spot and found black water and oil-soaked plants. Looking out at the damage from the spill, he mourned the loss of fish and vegetation.