CALGARY, Alberta (Reuters) - Enbridge Energy Partners LP has begun a new round of dredging on the Kalamazoo River, Michigan, to clean up oil from a huge pipeline spill in 2010, the U.S. Environmental Protection Agency said on Tuesday.

More than 20,000 barrels of heavy Canadian crude oil gushed into the Kalamazoo River system after multiple small corrosion-fatigue cracks caused the rupture of Line 6B in July 2010, the largest onshore oil spill in U.S. history.

Enbridge Energy Partners, the U.S. unit of Canada's largest pipeline company Enbridge Inc received an order from the EPA in March requiring more containment and recovery of oil from the spill. It has until the end of the year to complete the additional dredging.

Twelve miles of the Kalamazoo River near Marshall, Michigan, will be temporarily shut while Enbridge dredges approximately 350,000 cubic yards of contaminated sediment.

Over the past three years nearly 1.15 million gallons of oil have been recovered from the river.

The company was also fined $3.7 million by the U.S. Transportation Department's Pipeline and Hazardous Materials Safety Administration in July 2012.

Enbridge spokesman Larry Springer said the clean-up work would have no impact on Line 6B operations, which carries 231,000 barrels a day from Griffith, Indiana, to Sarnia, Ontario.

"This relates to the Marshall spill and has nothing to do with pipeline operations at all," Springer said.

(Reporting by Nia Williams; Editing by Carol Bishopric, Bernard Orr)