WASHINGTON — Members of several environmental groups delivered more than 781,000 signatures opposing construction of the Keystone XL pipeline to Senate leaders Tuesday.

Led by 350.org Policy Director Jason Kowalski and the Sierra Club’s Kate Colarulli, the activists carried 30 boxes intended to symbolize more than 20,000 signatures each to Capitol Hill. However, keeping in line with the environmentalists’ broader mission, the boxes were empty and did not contain the paperwork that would be produced by printing the hundreds of thousands of endorsements.

The activists swung by the Senate offices of Majority Leader Harry Reid and Minority Leader Mitch McConnell, whose staff accepted flash drives loaded with the full petition document.

TransCanada proposed the oil pipeline from Canada to Texas, but President Barack Obama decided to delay a decision on it until 2013, prompting Republicans to say he had caved to environmental interests in an election year. Environmentalists oppose the pipeline because they say it will endanger local wildlife and could pollute drinking water if there were a spill.

In a blog entry on the Huffington Post earlier Tuesday, environmentalist-author Bill McKibben explained the motivation behind the petition, which some have referred to as the “Keep Keystone Dead” petition.

“With rumors that Senate Democrats were starting to go mushy instead of backing their president, the leaders of every major environmental group in the country made a quick call over the weekend — they’d combine forces for a full-on day of pushing their members into action,” McKibben wrote.

Six hours and 54 minutes into Tuesday, the petition exceeded its original target of half a million signatures. By the time environmentalists congregated on Capitol Hill in the afternoon, the petition had been signed more than 781,000 times.