Marta Guttenberg stepped onto a wet Philadelphia sidewalk Tuesday to support a cause that's at once far-off and near - the American Indian-led effort to stop the Dakota Access Pipeline in the Midwest.

She and about 200 others commenced a loud, shouting march through Center City, waving signs and blocking traffic as part of a national day of protest. Rallies were planned in cities from New York to Spokane, Wash., aiming to stop a controversial oil pipeline near the Standing Rock Sioux Reservation.

"It's part of protection of water everywhere," said Guttenberg, 70, who lives in Center City. "I'm here to support the people of Standing Rock and their fight."

The $3.7 billion, 1,172-mile pipeline would cross four states, creating what backers say would be a clear economic good, and what opponents insist could be an environmental crisis.

"We are literally fighting for our future," said Ron Whyte, 34, of Philadelphia.

Demonstrators staged a "die in," lying in the street on John F. Kennedy Boulevard at 15th Street, portraying their "deaths" as the result of polluted water.

Police reported no arrests in a peaceful demonstration that traveled through Center City, stopping at banks and federal offices that endorse or fund the pipeline.

The pipeline would cross beneath the Missouri and Mississippi Rivers, as well as Lake Oahe near the Standing Rock reservation.

What began as a small, little-noticed protest in the Dakotas has grown into a movement with national support, driven largely by social media and the reporting of small news organizations and websites at the scene.

Locally, opposition has been led by Philly Solidarity with Standing Rock Sioux Defenders, an activist group.

"I've been taken aback by the support we've gotten in Philly," said a march organizer, Liz Ellis, 28, a visiting scholar at the University of Pennsylvania and a member of the Peoria tribe in Oklahoma.

Supporters include Greenpeace USA, the Sierra Club and the National Nurses Network, which has sent volunteers to provide first aid at the Standing Rock reservation, which covers parts of North and South Dakota.

American Indians and their supporters set up a large camp near Cannon Ball, N.D., that has drawn people and donations from around the country. Last month, 141 people were arrested during a tense standoff with police.

Near the Municipal Services Building, Ana Alonso, 21, of Philadelphia, helped hold a large banner that read, "Mni Wiconi" - which in the Lakota language means "water is life." She gazed at the crowd, a diverse collection of seniors and college students, black, white, Asian, and Indian.

"This is like the American Indian movement of the 1970s," said Alonso, a member of the Flathead nation in western Montana.

Marchers said they were opposing the pipeline - but also supporting clean water at a time when President-elect Donald Trump has denied the science of climate change and promised to expand production of coal, oil, and natural gas.

"We need to be out in the streets," a man shouted through a bullhorn. "We are going to have to disrupt."

The protest at Standing Rock, several marchers said, shows the potentially damaging intrusion of heavy industry into poorer communities. An early proposal would have routed the pipeline north of Bismarck, N.D., the Bismarck Tribune reported, but that was rejected partly because of the potential threat to the city's water supply.

"Pipelines always get moved to the places where the most vulnerable people live," said one demonstrator, Faith Zerbe, 42, the water-monitoring director at the Delaware Riverkeeper Network. "We're seeing the water protectors rise up in North Dakota."

Trine Smith, 46, of Philadelphia, said she was marching not just for herself but for future generations.

"We have a right to live," she said. "I'm a grandmother and a mother. And I'm worried about my children."