Klein was arrested alongside fellow Canadian Gitz Deranger, from the Athabasca Chipewyan First Nation, and several American native leaders on Day 13 of the protest.
"I have seen the devastation of our environment and people's health with increased cancer deaths," Deranger said before his arrest. "If Obama approves this pipeline, it would only lead to more of our people needlessly dying."
Bill Erasmus, chief of the Dene First Nation in the Northwest Territories, was there to lend support to those who were hauled off to D.C. police headquarters in armoured vans in the dying hours of a protest that has resulted in the arrests of more than 1,000 people.
Erasmus said the oilsands are already having a grim impact on the Slave River, which flows from northern Alberta into Great Slave Lake, NWT.
"We're downstream from the tarsands development; I live about 800 miles north and we're already feeling the effects," said Erasmus, who said water levels are dropping due to the mass amounts of water required to process the oilsands.
"Water is also being polluted ... we can no longer drink the water or eat the fish. We want the Obama administration to know this is not in the national interest of Canada, this is not in the national interest of the United States."
Keystone XL would carry Alberta oilsands crude from northern Alberta through six U.S. states to refineries in Texas.
As they have been every day for almost two weeks, the protesters were arrested one-by-one by U.S. Park Police and escorted to police vans after sitting peacefully on a White House sidewalk holding anti-pipeline banners. As they were helped into police vans, their fellow activists shouted "thank you" on the other side of the police barricades.
Friday's arrests came a week after the U.S. State Department released its final environmental assessment of the $7 billion pipeline, determining the project would cause minimal risk. Energy Secretary Steven Chu also suggested this week that the pipeline was likely to get approved due to Canada's close ties to the United States.
While Daryl Hannah and Margot Kidder, both arrested during the two-week campaign, aren't exactly at the height of their celebrity, former vice-president Al Gore, now a leading American environmentalist, has also weighed in.
In a plea to Obama earlier this week, Gore urged the president this week to block the pipeline, calling the oilsands "the dirtiest fuel on the planet."
"The answer to our climate, energy and economic challenges does not lie in burning more dirty fossil fuels — instead, we must continue to press for much more rapid development of renewable energy and energy efficient technologies and cuts in the pollution that causes global warming," Gore wrote on his blog.
The Obama administration says it will make a final decision on the pipeline by the end of the year, after it determines whether the project is in the U.S. national interest.
Opposing the pipeline has become a rallying cry for the American environmental movement in the aftermath of failed federal climate change legislation last year. Obama's liberal base has warned him that approving the pipeline could cost him their votes.
Environmentalists say the pipeline is a disaster waiting to happen, pointing to several recent oil spills along pipelines in the past few months. Advocates for the project say it will create thousands of jobs and help end U.S. reliance on Middle Eastern oil.