As she walked her dog along a Southwest Washington beach, Ellen Anderson made a surprising discovery — hundreds of pieces of foam insulation that had washed up on shore.

Some were chunky gold blocks. Others were blue slabs or smaller, white pieces of what appeared to be Styrofoam.

So Anderson, an Ocean Park retiree who is a founding member of the Grassroots Garbage Gang that picks up trash on beaches, went to work. During two days this month, she collected more than 650 pieces of foam from a one-mile stretch of beach.

By comparison, Anderson found about 10 pieces of foam on that stretch of beach during a cleanup day in 2010.

Federal officials say it's reasonable to assume much of the foam, which floats high in the water and can catch the wind, is some of the first debris from Japan's calamitous March 11, 2011, tsunami to show up on U.S. beaches.

"This is consistent with what our models show," said Nir Barnea, a National Oceanic and Atmospheric Administration (NOAA) official who has helped track the debris.

Though not as impressive as the 66-foot-long dock from Japan that washed ashore on an Oregon beach last week, the foam is a ubiquitous presence on stretches of Northwest shorelines.

"It's not glitzy, and it's not glamorous, but it's everywhere," Anderson said.

It's hard to predict how much debris might show up or where it might end up.

Rough estimates from the Japanese government indicate the tsunami washed away some 5 million tons of material.

Most of it sank right way, but 1.5 million tons of trash was buoyant enough to float. Some portion of that debris is expected to come ashore in Alaska and on the West Coast during the next year or longer.

In Washington, increased amounts of debris have been reported on some beaches from Moclips, Grays Harbor County, south to the Columbia River, according to Steve Brand, a field operation manager with Washington State Parks.

A volunteer with the Grassroots Garbage Gang counted more than 6,700 pieces of foam along a 13-mile stretch of beach during a survey Sunday.

The yellow and blue insulation foam is quite stiff. Some pieces have what appears to be marks left by glue that might have been used to attach it to containers or buildings.

The white foam crumbles much more in the grinding of the surf.

As it disintegrates into smaller, beadlike pieces, the material can be ingested by birds as well as marine organisms.

The Grassroots Garbage Gang already has begun a foam cleanup on the Long Beach Peninsula. This is in addition to three annual community beach cleanups, including a July 5 event that targets debris from fireworks.

If the foam becomes a chronic problem, it will be difficult to deal with it.

"We will be stretched to the limit," said Shelly Pollock, a cleanup organizer. "If it keeps happening, we are going to need assistance."

Pollock says she hopes the tsunami debris will spur broader awareness of the problems of marine debris.

State officials in Washington and Oregon are working with other organizations to develop plans to help support volunteer cleanups. In Washington, the state Department of Ecology has set aside about $100,000 for disposal costs.

"It's not a lot of money, and we want to make sure that groups check first and see if we can assist them," said Linda Kent, an agency spokeswoman.

It's unclear just what kinds of materials might make the voyage across the Pacific.

The dock that arrived in Oregon last week had been sitting for years in Japan's coastal waters and was covered with marine life. That spurred concerns that debris could carry invasive species to the Northwest.

A refrigerator found late last week on Nedonna Beach in Oregon was filled with gooseneck barnacles that had hitched a ride in the ocean.

But those barnacles already are present in Northwest waters and not considered a problem, according to Oregon state Department of Fish and Wildlife officials who identified the barnacles attached to the refrigerator.

Hal Bernton: 206-464-2581

or hbernton@seattletimes.com