Organizers are calling it the largest environmental protest in American history.

They say more than 35,000 people showed up in front of the Washington Monument Sunday in hopes of persuading President Barrack Obama to make good on his recent promises to combat climate change.

At issue is the approval of the Keystone XL Pipeline, which would ship Alberta bitumen to the Gulf Coast for refinement.

Long delays from within the Obama administration have hampered Calgary-based TransCanada’s efforts to get Alberta oil to market in the states.

Environmental activists, movie stars and First Nation’s leaders addressed the crowd, including BC’s Jackie Thomas who is worried aboriginal environmental concerns are falling on deaf ears.

She says, “First Nation’s are always expected to be the sacrificial lambs, like the economy is a human being, like the economy is more important than our land or our water.”  

Nathan Lemphers with the Pembina Institute agrees, and says politicians seem to be blinded by the pipeline’s temporary monetary gains and don’t look at the long term costs.

“They don’t necessarily link pipelines like this and its climate liabilities that are associated with it with the climate costs of inaction with climate change,” says Lemphers.  

A similar protest in 2012 led to Obama to postponing the controversial Keystone decision until after the November presidential election.