A barge carrying 1 million pounds of debris that washed up on Alaska and Canada coastlines — half of it from the 2011 Japan tsunami — signals a larger cleanup that needs to be done.

A barge docked in Georgetown stretches the size of a football field and is piled high with 3,400 large white sacks of marine debris — buckets, water bottles, nets and even shoes.

In total, the barge tied up at Waste Management’s Duwamish facility holds about 1 million pounds of trash, roughly half of which is debris from the 2011 Japan tsunami that found its way onto Alaskan and Canadian shores.

Despite its enormity, the trash represents less than 1 percent of the debris littering the Alaska coastline, said Chris Pallister, co-founder of Gulf of Alaska Keeper, a nonprofit that works to clean up the coastline there.

“It’s one of the greatest environmental tragedies on the planet right now,” Pallister said.

The barge arrived in Seattle on Thursday at the end of a $1 million project funded mostly by Japan to clean up Alaskan and Canadian shorelines in the aftermath of the massive earthquake and tsunami.

Japan estimates that 5 million tons of debris washed out to sea in the tsunami. Most of it sank in the first few miles, leaving an estimated 1.5 million tons floating in the Pacific.

Even without a natural disaster, winds and currents routinely deposit large amounts of debris on Alaskan beaches, said Peter Murphy, Alaska regional coordinator of the National Oceanic and Atmospheric Administration (NOAA) Marine Debris Program.

Next month, the trash that arrived in Seattle this week will be sorted by volunteers coordinated by the nonprofit Parley for the Oceans. Unusable debris will be sent to the Columbia Ridge landfill at Arlington, Ore., while most of the plastic will be recycled.

Alaska’s shoreline stretches 44,000 miles, more than double the length of the East and West coasts combined.

With so much beachfront, and some areas of steep shorelines and cliffs, it’s not easy to get the debris out. So once the trash was collected and bagged on the beaches, Pallister used helicopters to lift the sacks to the barge.

Advocates for clean shorelines faced another hurdle last year when, due to a lack of capacity, Anchorage’s landfill stopped accepting marine debris unless it was in small pieces, Pallister said.

Getting the barge safely to Seattle was a milestone in itself, Pallister said.

“It’s a real sense of relief that this is here,” he said.

It first stopped in Kodiak, Alaska, on July 15. From there it traveled to 10 other sites, including Montague Island near Prince William Sound and Gore Point on the Kenai Peninsula.

Pallister’s plan for coordinated barge stops to pick up debris at multiple locations was unprecedented, Murphy said.

Supporters of the project, including NOAA, Waste Management and the Alaska Department of Environmental Conservation, all agree on one thing: The coasts need to be cleaned.

Most of the debris on the barge is from Alaska, with refuse from just one British Columbia site — Ucluelet, on Vancouver Island. Karla Robison, the manager of environmental and emergency services in Ucluelet, called on more Canadian cities to step up to help clean the coasts.

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Japan has provided $5 million to the U.S. for tsunami debris removal. Alaska received $2.5 million of that, using it on this project and other, smaller efforts to clean up coastlines and complete aerial surveys.

Janna Stewart, the tsunami marine-debris coordinator for Alaska’s environmental-conservation department, said she hopes the state can receive another $1 million left in the $5 million pot to continue the cleanup.

In terms of efficiency and safety, the project has been a success, she said.

Pallister knows there’s much more debris to be removed — but progress has been made.

“It’s not completely bleak,” he said. “There is some light way out there. It’s a flicker, but it’s out there.”