EXPLAINER: Why a rural pipeline is a climate battleground

As Enbridge Energy prepares to finish rebuilding an oil pipeline across rural northern Minnesota, protesters are occupying part of the construction area and pledging a “summer of resistance” on the ground and in court.

Enbridge, which has obtained all necessary state and federal permits for the Line 3 project, says it will be finished by year's end.

The Canadian company describes it as essential for reliable oil supplies in both nations, saying the plan has undergone rigorous environmental permitting and will boost Minnesota's economy. Opponents contend it endangers waterways, violates indigenous treaty rights and abets dependence on fossil fuels that will further overheat the planet.

What's beyond dispute is that the project fits into an escalating battle over the future of energy pipelines, which federal regulators say are generally safer than hauling fuels by rail or highway but pose their own hazards, particularly spills in ecologically sensitive places.

WHAT IS THE LINE 3 PROJECT?

The 1,097-mile (1,765-kilometer) line is part of an Enbridge network that moves oil from fields in Canada's Alberta province to refineries in southern Ontario and the U.S. Midwest. It crosses the far northeastern tip of North Dakota, then cuts through northern Minnesota to a terminal at Superior, Wisconsin.

The line carries nearly 16.4 million gallons (62 million liters) of oil used in fuels and other products.

Enbridge says the original 1960s pipe is deteriorating and carrying about half its capacity. The company is replacing it with pipe made of stronger steel that it says would enable resumption of a normal flow — about 32 million gallons (121 million liters) daily.

Work is finished in Canada, North Dakota and Wisconsin and 60% complete in Minnesota, where 337 miles (542 kilometers)...